JP2016082236A - LIGHT EMITTING ELEMENT, DISPLAY DEVICE, ELECTRONIC DEVICE, AND LIGHTING DEVICE - Google Patents

Abstract

A light-emitting element having high emission efficiency in a light-emitting element having a fluorescent material as a light-emitting substance is provided.
A light-emitting element having a pair of electrodes and an EL layer provided between the pair of electrodes. The EL layer includes a host material and a guest material. The host material has a function capable of exhibiting thermally activated delayed fluorescence at room temperature, and the guest material has a function capable of exhibiting fluorescence. The second excited triplet energy level of the guest material is equal to or higher than the lowest excited singlet energy level of the guest material.
[Selection] Figure 1

Description

  One embodiment of the present invention relates to a light-emitting element in which a light-emitting layer that can emit light by applying an electric field is sandwiched between a pair of electrodes, or a display device, an electronic device, and a lighting device each having the light-emitting element.

  Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. Alternatively, one embodiment of the present invention relates to a process, a machine, a manufacture, or a composition (composition of matter). Therefore, the technical field of one embodiment of the present invention disclosed in this specification more specifically includes a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a power storage device, a memory device, a driving method thereof, Alternatively, the production method thereof can be given as an example.

  In recent years, research and development of light-emitting elements using electroluminescence (EL) have been actively conducted. The basic structure of these light-emitting elements is such that a layer containing a light-emitting substance (EL layer) is sandwiched between a pair of electrodes. Light emission from a light-emitting substance can be obtained by applying a voltage between the electrodes of this element.

  Since the above light-emitting element is a self-luminous type, a display device using the light-emitting element has advantages such as excellent visibility, no need for a backlight, and low power consumption. Furthermore, it has advantages such as being thin and light and capable of high response speed.

  In the case of a light-emitting element (for example, an organic EL element) in which an organic material is used as a light-emitting material and an EL layer including the light-emitting material is provided between a pair of electrodes, a voltage is applied between the pair of electrodes so that electrons are emitted from the cathode. However, holes are injected from the anode into the light-emitting EL layer, and current flows. Then, when the injected electrons and holes are recombined, the light-emitting organic material becomes an excited state, and light emission can be obtained from the excited light-emitting organic material.

The types of excited states formed by organic materials include singlet excited states (S ^* ) and triplet excited states (T ^* ). Light emitted from singlet excited states is fluorescent, and light emitted from triplet excited states is emitted. It is called phosphorescence. Further, the statistical generation ratio thereof in the light emitting element is S ^* : T ^* = 1: 3. Therefore, a light emitting element using a phosphorescent material can obtain higher light emission efficiency than a light emitting element using a fluorescent material. Therefore, development of a light-emitting element using a phosphorescent material capable of converting a triplet excited state into light emission has been actively performed in recent years.

  Further, as a material capable of converting a part of the triplet excited state into light emission, a thermally activated delayed fluorescence (TADF) body is known. In the thermally activated delayed phosphor, a singlet excited state is generated from the triplet excited state by crossing between the reverse terms, and converted from the singlet excited state to light emission. Patent Documents 1 and 2 disclose materials that emit thermally activated delayed fluorescence.

  In order to increase the light emission efficiency of a light-emitting device using a thermally activated delayed phosphor, not only a singlet excited state is efficiently generated from a triplet excited state but also a singlet excited in the thermally activated delayed phosphor. It is important that luminescence can be efficiently obtained from the state, that is, that the fluorescence quantum yield is high. However, it is difficult to design a light-emitting material that satisfies these two simultaneously.

  Therefore, in a light emitting device having a thermally activated delayed phosphor and a material that emits fluorescence, the singlet excitation energy of the thermally activated delayed phosphor is transferred to the material that emits fluorescence, and light is emitted from the material that emits fluorescence. Has been proposed (see Patent Document 3).

JP 2004-241374 A JP 2006-24830 A JP 2014-45179 A

  In a light-emitting element having a thermally activated delayed phosphor and a fluorescent material, in order to increase the light emission efficiency, a singlet excited state is efficiently generated from a triplet excited state in the thermally activated delayed phosphor. This is very important. Further, it is important that the excitation energy is efficiently transferred from the singlet excited state of the thermally activated delayed phosphor to the singlet excited state of the fluorescent material. In addition, it is important that light emission can be efficiently obtained from a singlet excited state of a fluorescent material, that is, that the fluorescent quantum yield of the fluorescent material is high.

  A material that emits fluorescence from the triplet excited state of the thermally activated delayed phosphor when the excitation energy efficiently moves from the singlet excited state of the thermally activated delayed phosphor to the singlet excited state of the material that emits fluorescence. Excitation energy may also move to the triplet excited state. When excitation energy is transferred from the triplet excited state of the thermally activated delayed phosphor to the triplet excited state of the fluorescent material, a singlet excited state is generated from the triplet excited state in the thermally activated delayed phosphor. Probability decreases. Therefore, in order to increase the light emission efficiency of the light emitting element, it is important to prevent the excitation energy from moving from the triplet excited state of the thermally activated delayed phosphor to the triplet excited state of the fluorescent material. .

  An object of one embodiment of the present invention is to provide a light-emitting element with high emission efficiency in a light-emitting element including a fluorescent material as a light-emitting material. Another object of one embodiment of the present invention is to provide a light-emitting element with high reliability. Another object of one embodiment of the present invention is to provide a light-emitting element with high emission efficiency and high reliability. Another object of one embodiment of the present invention is to provide a novel light-emitting element. Another object of one embodiment of the present invention is to provide a novel light-emitting element with high emission efficiency and low power consumption.

  Note that the description of the above problems does not disturb the existence of other problems. Note that one embodiment of the present invention does not necessarily have to solve all of these problems. Problems other than those described above are naturally apparent from the description of the specification and the like, and it is possible to extract problems other than the above from the description of the specification and the like.

  One embodiment of the present invention is a light-emitting element including a pair of electrodes and an EL layer provided between the pair of electrodes. The EL layer includes a host material and a guest material. Has a function capable of exhibiting thermally activated delayed fluorescence at room temperature, the guest material has a function capable of exhibiting fluorescence, and the second excited triplet energy level of the guest material is The light-emitting element has a lowest excited singlet energy level or higher.

  Another embodiment of the present invention is a light-emitting element including a pair of electrodes and an EL layer provided between the pair of electrodes, and the EL layer includes a host material and a guest material. The host material has a function capable of exhibiting thermally activated delayed fluorescence at room temperature, the guest material has a function capable of exhibiting fluorescence, and the second excited triplet energy level of the guest material is The light-emitting element is characterized in that the host material has a lowest excited triplet energy level or higher, and the host material has a lowest excited triplet energy level or higher than the guest material's lowest excited triplet energy level. .

  In the above structure, the second excited triplet energy level of the guest material is preferably equal to or higher than the lowest excited singlet energy level of the host material.

  In each of the above structures, the difference between the lowest excited triplet energy level of the host material and the lowest excited triplet energy level of the guest material is preferably 0.5 eV or more.

  In each of the above structures, the emission energy of thermally activated delayed fluorescence of the host material is preferably equal to or higher than the phosphorescence emission energy of the guest material.

  In the above structure, the difference between the thermally activated delayed fluorescence emission energy of the host material and the phosphorescence emission energy of the guest material is preferably 0.5 eV or more.

  Another embodiment of the present invention is a light-emitting element including a pair of electrodes and an EL layer provided between the pair of electrodes, and the EL layer includes a host material and a guest material. The host material has a function capable of exhibiting thermally activated delayed fluorescence at room temperature, the guest material has a function capable of exhibiting fluorescence, and the second excited triplet energy level of the guest material is The light-emitting element is characterized in that the host material has a lowest excited triplet energy level of the host material, and the host material has a lowest excited triplet energy level of not less than the lowest excited singlet energy level of the guest material. .

  In the above structure, the second excited triplet energy level of the guest material is preferably equal to or higher than the lowest excited singlet energy level of the host material.

  In each of the above structures, it is preferable that the emission energy of the thermally activated delayed fluorescence of the host material is equal to or higher than the fluorescence emission energy of the guest material.

  In each of the above structures, the difference between the lowest excited singlet energy level of the host material and the lowest excited triplet energy level of the host material is preferably more than 0 eV and 0.2 eV or less.

  Another embodiment of the present invention is a light-emitting element including a pair of electrodes and an EL layer provided between the pair of electrodes, and the EL layer includes a host material and a guest material. The host material includes a first organic compound and a second organic compound, and the exciplex formed by the first organic compound and the second organic compound is thermally active at room temperature. The guest material has a function capable of exhibiting fluorescence, and the second excited triplet energy level of the guest material is the lowest excited singlet energy level of the guest material. It is a light emitting element characterized by being above the order.

  Another embodiment of the present invention is a light-emitting element including a pair of electrodes and an EL layer provided between the pair of electrodes, and the EL layer includes a host material and a guest material. The host material includes a first organic compound and a second organic compound, and the exciplex formed by the first organic compound and the second organic compound is thermally active at room temperature. The guest material has a function capable of exhibiting fluorescence, and the second excited triplet energy level of the guest material is the lowest excited triplet energy level of the exciplex. And the lowest excited triplet energy level of the exciplex is equal to or higher than the lowest excited triplet energy level of the guest material.

  In the above structure, the second excited triplet energy level of the guest material is preferably equal to or higher than the lowest excited singlet energy level of the exciplex.

  In each of the above structures, the difference between the lowest excited triplet energy level of the exciplex and the lowest excited triplet energy level of the guest material is preferably 0.5 eV or more.

  In each of the above structures, the emission energy of the thermally activated delayed phosphor of the exciplex is preferably greater than or equal to the phosphorescence emission energy of the guest material.

  In the above structure, the difference between the emission energy of the thermally activated delayed phosphor of the exciplex and the phosphorescence emission energy of the guest material is preferably 0.5 eV or more.

  Another embodiment of the present invention is a light-emitting element including a pair of electrodes and an EL layer provided between the pair of electrodes, and the EL layer includes a host material and a guest material. The host material includes a first organic compound and a second organic compound, and the exciplex formed by the first organic compound and the second organic compound is thermally active at room temperature. The guest material has a function capable of exhibiting fluorescence, and the second excited triplet energy level of the guest material is the lowest excited triplet energy level of the exciplex. And the lowest excited triplet energy level of the exciplex is equal to or higher than the lowest excited singlet energy level of the guest material.

  In the above structure, the second excited triplet energy level of the guest material is preferably equal to or higher than the lowest excited singlet energy level of the exciplex.

  Moreover, in each said structure, it is preferable that the emission energy of the heat activation delayed fluorescence of an exciplex is more than the fluorescence emission energy of a guest material.

  In each of the above structures, the difference between the lowest excited singlet energy level of the exciplex and the lowest excited triplet energy level of the exciplex is preferably greater than 0 eV and 0.2 eV or less.

  In each of the above structures, the guest material preferably emits light.

  In each of the above structures, the guest material is selected from one or more skeletons selected from anthracene, tetracene, chrysene, pyrene, perylene, and acridone, and aromatic amines, alkyl groups, and aryl groups. It is preferable to have the above substituents.

  In the above structure, the skeleton is preferably bonded to the substituent.

  In the above structure, the skeleton is preferably bonded to the two substituents and the substituents have the same structure.

  Another embodiment of the present invention is a display device including the light-emitting element having any of the above structures and a color filter, a seal, or a transistor. Another embodiment of the present invention is an electronic device including the display device and a housing or a touch sensor. Another embodiment of the present invention is a lighting device including the light-emitting element having any of the above structures and a housing or a touch sensor.

  According to one embodiment of the present invention, a light-emitting element having high emission efficiency can be provided as a light-emitting element including a material that emits fluorescence as a light-emitting material. Alternatively, according to one embodiment of the present invention, a highly reliable light-emitting element can be provided. Alternatively, according to one embodiment of the present invention, a light-emitting element with high emission efficiency and high reliability can be provided. Alternatively, according to one embodiment of the present invention, a novel light-emitting element can be provided. Alternatively, according to one embodiment of the present invention, a novel light-emitting element with high emission efficiency and reduced power consumption can be provided.

  Note that the description of these effects does not disturb the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. It should be noted that the effects other than these are naturally obvious from the description of the specification, drawings, claims, etc., and it is possible to extract the other effects from the descriptions of the specification, drawings, claims, etc. It is.

FIGS. 3A and 3B are a schematic cross-sectional view of a light-emitting element of one embodiment of the present invention and a schematic diagram illustrating correlation of energy levels. FIGS. 6A and 6B illustrate transient fluorescence characteristics of a host material according to one embodiment of the present invention. FIGS. 3A and 3B are a schematic cross-sectional view of a light-emitting layer of a light-emitting element of one embodiment of the present invention and a schematic diagram illustrating correlation of energy levels. FIGS. FIGS. 3A and 3B are a cross-sectional schematic diagram illustrating a light-emitting element of one embodiment of the present invention and a diagram illustrating a correlation between energy levels in a light-emitting layer. FIGS. FIGS. 3A and 3B are a cross-sectional schematic diagram illustrating a light-emitting element of one embodiment of the present invention and a diagram illustrating a correlation between energy levels in a light-emitting layer. FIGS. 4A and 4B are a block diagram and a circuit diagram illustrating a display device of one embodiment of the present invention. FIG. 6 is a perspective view illustrating an example of a touch panel of one embodiment of the present invention. FIGS. 5A and 5B are cross-sectional views illustrating an example of a display device and a touch sensor of one embodiment of the present invention. FIG. 6 is a cross-sectional view illustrating an example of a touch panel of one embodiment of the present invention. 4A and 4B are a block diagram and a timing chart of a touch sensor of one embodiment of the present invention. FIG. 6 is a circuit diagram of a touch sensor of one embodiment of the present invention. FIG. 10 is a perspective view illustrating a display module of one embodiment of the present invention. 6A and 6B illustrate an electronic device of one embodiment of the present invention. FIG. 10 illustrates a lighting device of one embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and various changes can be made in form and details without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below.

  Note that the position, size, range, and the like of each component illustrated in the drawings and the like may not represent the actual position, size, range, or the like for easy understanding. Therefore, the disclosed invention is not necessarily limited to the position, size, range, or the like disclosed in the drawings and the like.

  In this specification and the like, the ordinal numbers attached as the first and second are used for convenience and may not indicate the order of steps or the order of lamination. Therefore, for example, the description can be made by appropriately replacing “first” with “second” or “third”. In addition, the ordinal numbers described in this specification and the like may not match the ordinal numbers used to specify one embodiment of the present invention.

  Further, in this specification and the like, in describing the structure of the invention with reference to drawings, the same reference numerals may be used in common among different drawings.

  In this specification and the like, the terms “film” and “layer” can be interchanged with each other. For example, the term “conductive layer” may be changed to the term “conductive film”. Alternatively, for example, the term “insulating film” may be changed to the term “insulating layer” in some cases.

  In this specification and the like, a singlet excited state is a singlet state having excitation energy. Of the singlet excited states, the excited state having the lowest energy is referred to as the lowest excited singlet state.

  In this specification and the like, a singlet excitation energy level is an energy level of a singlet excited state. Of the singlet excitation energy levels, the lowest excitation energy level is referred to as the lowest excitation singlet energy level.

  In this specification and the like, a triplet excited state is a triplet state having excitation energy. Of the triplet excited states, the excited state having the lowest energy is referred to as the lowest excited triplet state. An excited state having higher energy than the lowest excited triplet state among triplet excited states is referred to as a highly excited triplet state. In addition, the excited state having the lowest energy among the highly excited triplet states is referred to as a second excited triplet state.

  In this specification and the like, a triplet excitation energy level is an energy level of a triplet excited state. Of the triplet excitation energy levels, the lowest excitation energy level is referred to as the lowest excitation triplet energy level. Among triplet excitation energy levels, an energy level higher than the lowest excitation triplet energy level is referred to as a high excitation triplet energy level. Moreover, the lowest energy level among the high excitation triplet energy levels is referred to as a second excitation triplet energy level.

  In this specification and the like, a fluorescent material is a material that emits light in the visible light region when relaxing from a singlet excited state to a ground state. A phosphorescent material is a material that emits light in the visible light region at room temperature when relaxing from a triplet excited state to a ground state. In other words, a phosphorescent material is one of materials that can convert triplet excitation energy into visible light.

  In addition, in this specification and the like, a thermally activated delayed phosphor refers to a material that can generate a singlet excited state from a triplet excited state by reverse intersystem crossing by thermal activation. The thermally activated delayed phosphor may include a material that can generate a singlet excited state by a cross-reciprocal crossover from a triplet excited state alone, such as a material that emits TADF. Further, a combination of two kinds of materials forming an exciplex (also referred to as an exciplex or an exciplex) may be included.

  The thermally activated delayed phosphor can be said to be a material having a triplet excited state and a singlet excited state close to each other. More specifically, a material in which the difference between the energy levels of the triplet excited state and the singlet excited state exceeds 0 eV and is 0.2 eV or less is preferable. That is, the difference between the energy levels of the triplet excited state and the singlet excited state exceeds 0 eV in a material that can generate a singlet excited state by reverse intersystem crossing from a triplet excited state alone, such as a material that emits TADF. It is preferable that the difference between the triplet excited state and the singlet excited state in the exciplex is greater than 0 eV and not greater than 0.2 eV.

  In this specification and the like, the emission energy of thermally activated delayed fluorescence is the emission peak (including shoulder) on the shortest wavelength side of thermally activated delayed fluorescence. In this specification and the like, the phosphorescence energy or triplet excitation energy is a phosphorescence peak (including a shoulder) on the shortest wavelength side of phosphorescence. The phosphorescence emission can be observed by performing a time-resolved photoluminescence method in a low temperature (for example, 10K) environment.

  Note that in this specification and the like, room temperature refers to any temperature of 0 ° C. to 40 ° C.

(Embodiment 1)
In this embodiment, a light-emitting element of one embodiment of the present invention will be described below with reference to FIGS.

<1. Configuration Example 1 of Light-Emitting Element>
First, the structure of the light-emitting element of one embodiment of the present invention is described below with reference to FIGS.

  FIG. 1A is a schematic cross-sectional view of a light-emitting element 150 of one embodiment of the present invention.

  The light-emitting element 150 includes an EL layer 100 provided between a pair of electrodes (the electrode 101 and the electrode 102). The EL layer 100 includes at least a light emitting layer 130. Note that in this embodiment mode, the electrode 101 is used as an anode and the electrode 102 is used as a cathode.

  In addition to the light-emitting layer 130, the EL layer 100 illustrated in FIG. 1A includes each functional layer, and each functional layer includes a hole injection layer 111, a hole transport layer 112, an electron transport layer 117, And an electron injection layer 118. Note that the structure of the EL layer 100 is not limited to the structure shown in FIG. 1A, and is selected from the hole injection layer 111, the hole transport layer 112, the electron transport layer 117, and the electron injection layer 118. What is necessary is just to set it as the structure which has at least one. Alternatively, the EL layer 100 can reduce a hole or electron injection barrier, improve a hole or electron transport property, inhibit a hole or electron transport property, or suppress a quenching phenomenon caused by an electrode. It is good also as a structure which has a functional layer which has these functions.

  FIG. 1B is a schematic cross-sectional view illustrating an example of the light-emitting layer 130 illustrated in FIG. A light-emitting layer 130 illustrated in FIG. 1B includes a host material 131 and a guest material 132.

  The host material 131 preferably has a function of converting triplet excitation energy into singlet excitation energy by reverse intersystem crossing. By doing so, part of the triplet excitation energy generated in the light-emitting layer 130 is converted into singlet excitation energy by the host material 131 and moved to the guest material 132, so that it can be extracted as fluorescence. . For this purpose, the difference between the lowest excited singlet energy level of the host material 131 and the lowest excited triplet energy level of the host material 131 is preferably more than 0 eV and not more than 0.2 eV. In particular, the host material 131 is preferably a substance that exhibits thermally activated delayed fluorescence at room temperature, that is, a thermally activated delayed phosphor.

  The host material 131 may be composed of a single material or a plurality of materials. The guest material 132 may be a light-emitting organic material, and the light-emitting organic material is preferably a material that can emit fluorescence (hereinafter also referred to as a fluorescent material). In the following description, a structure using a fluorescent material as the guest material 132 will be described. Note that the guest material 132 may be read as a fluorescent material.

<< 1-1. Light emitting mechanism of light emitting element >>
First, the light emission mechanism of the light emitting element 150 will be described below.

  In the light-emitting element 150 of one embodiment of the present invention, when a voltage is applied between the pair of electrodes (the electrode 101 and the electrode 102), electrons from the cathode and holes from the anode are applied to the EL layer 100, respectively. It is injected and current flows. Then, when the injected electrons and holes are recombined, the guest material 132 in the light-emitting layer 130 included in the EL layer 100 is excited, and light emission can be obtained from the excited guest material 132.

Note that light emission from the guest material 132 is obtained by the following two processes.
(Α) Direct recombination process (β) Energy transfer process

<< 1-2. (Α) Direct recombination process »
First, the direct recombination process in the guest material 132 will be described. Carriers (electrons or holes) recombine in the guest material 132, and an excited state of the guest material 132 is formed. At this time, when the guest material 132 is in a singlet excited state, fluorescence is emitted. On the other hand, when the excited state of the guest material 132 is a triplet excited state, it is thermally deactivated.

  In the above-described (α) direct recombination process, if the guest material 132 has a high fluorescence quantum yield, light is efficiently emitted from the singlet excited state of the guest material 132. However, the triplet excited state of the guest material 132 does not contribute to light emission due to thermal deactivation.

<< 1-3. (Β) Energy transfer process »
Next, in order to describe the energy transfer process of the host material 131 and the guest material 132, FIG. 1C is a schematic diagram illustrating the correlation of energy levels. In addition, the notation and code | symbol in FIG.1 (C) are as follows.
Host (131): Host material 131
Guest (132): Guest material 132 (fluorescent material)
S _H : lowest excited singlet energy level of host material 131 T _H : lowest excited triplet energy level of host material 131 S _1G : lowest excited singlet energy level of guest material 132 (fluorescent material) T _1G : lowest excited triplet energy level of guest material 132 (fluorescent material) T _2G : second excited triplet energy level of guest material 132 (fluorescent material)

Carriers recombine in the host material 131, and an excited state of the host material 131 is formed. In this case, the excited state of the host material 131 is a singlet excited state, and, _{S H} of the host material 131, is equal to or greater than _{S 1G} of the guest material 132, as shown in route _{E 1} shown in FIG. 1 (C) In addition, the singlet excitation energy of the host material 131 moves from the host material 131 to the guest material 132, and the guest material 132 is in a singlet excited state. The guest material 132 in a singlet excited state exhibits fluorescence.

  Note that in the energy transfer from the singlet excited state of the host material 131 to the triplet excited state of the guest material 132, direct transition from the singlet ground state to the triplet excited state in the guest material 132 is prohibited. Since it is difficult to become the main energy transfer process, it is omitted here. That is, energy transfer from the singlet excited state of the host material 131 to the singlet excited state of the guest material 132 is important as represented by the following general formula (G1).

¹ H ^* + ¹ G → ¹ H + ¹ G ^* (G1)

Note that in General Formula (G1), ¹ H ^* represents the lowest excited singlet state of the host material 131, ¹ G represents a singlet ground state of the guest material 132, and ¹ H represents a singlet ground state of the host material 131 ¹ G ^* represents the lowest excited singlet state of the guest material 132.

Therefore, when the excited state of the host material 131 is a singlet excited state, the lowest excited singlet energy level (S _H ) of the host material 131 is equal to or higher than the lowest excited singlet energy level (S _1G ) of the guest material 132. Is preferable.

  Next, when an excited state of the host material 131 is generated and is a triplet excited state, fluorescence emission is obtained by following the following two processes.

Since the host material 131 has a function of converting a part of triplet excitation energy to singlet excitation energy by reverse intersystem crossing, first, as a first process, a route A _{1 in} FIG. as shown in, by reverse intersystem crossing from T _H of the host material 131 (up-conversion), the excitation energy into S _H moves.

As the second step subsequent, _{S H} of the host material 131, is equal to or greater than _{S 1G} of the guest material 132, as shown in route _{E 1} in FIG. 1 (C), the guest from the _{S H} of the host material 131 Excitation energy is transferred to S _1G of the material 132, and the guest material 132 is in a singlet excited state. Fluorescence emission is obtained from the guest material 132 in a singlet excited state.

  The first process and the second process described above are represented by the following general formula (G2).

³ H ^* + ¹ G → (reverse intersystem ^{crossing) → 1 H * + 1 G} → 1 H + 1 G * (G2)

Note that in General Formula (G2), ³ H ^* represents the lowest excited triplet state of the host material 131, ¹ G represents the singlet ground state of the guest material 132, and ¹ H ^* represents the lowest excited singlet of the host material 131. ¹ H represents the singlet ground state of the host material 131, and ¹ G ^* represents the lowest excited singlet state of the guest material 132.

As shown in the general formula (G2), the lowest excited singlet state ( ¹ H ^* ) of the host material 131 is generated by reverse intersystem crossing from the lowest excited triplet state ( ³ H ^* ) of the host material 131, and then The excitation energy is transferred to the lowest excited singlet state ( ¹ G ^* ) of the guest material 132.

If all of the energy transfer processes described in the above (β) energy transfer process occur efficiently, both the triplet excitation energy and the singlet excitation energy of the host material 131 are efficiently reduced to the lowest excited singlet state of the guest material 132. Since it is converted to ( ¹ G ^* ), highly efficient light emission is possible.

However, if the host material 131 is deactivated by releasing the excitation energy as light or heat before the excitation energy moves from the singlet excited state of the host material 131 to the singlet excited state of the guest material 132, Luminous efficiency will fall. Furthermore, it as previous processes, the efficiency of the process of A ₁ crossing between Gyakuko the singlet excited state from a triplet excited state in the host material 131 falls, also the luminous efficiency is lowered. In particular, _{T H} of the host material 131 is lower than the _{T 1G} of the guest material 132, to become a _{S H ≧ S 1G> T 1G} > T H, the energy difference between _{T H} and _{S H} is increased . As a result, the reverse intersystem crossing of the route A ₁ in FIG. 1C is less likely to occur, so the subsequent energy transfer process shown in the route E ₁ is also reduced, and the generation efficiency of the singlet excited state of the guest material 132 is reduced. To do. Therefore, the lowest excited triplet energy level (T _H ) of the host material 131 is preferably _{equal to} or higher than the lowest excited triplet energy level (T _1G ) of the guest material 132.

Incidentally, as shown in route _{E 2} in FIG. 1 (C), even if _{the T 1G} to excitation energy of the guest material 132 from _{T H} of the host material 131 is moved, to heat inactivation. Therefore, it is possible to it is less energy transfer process shown in Route E ₂ shown in FIG. 1 (C) is, it is possible to reduce the production efficiency of the triplet excited state of the guest material 132 reduces the thermal inactivation, preferable. For this purpose, the concentration of the guest material 132 with respect to the host material 131 is preferably low.

  In addition, when the direct recombination process in the guest material 132 becomes dominant, a large number of triplet excited states of the guest material 132 are generated in the light emitting layer, and the light emission efficiency is impaired due to thermal deactivation. That is, when the ratio of the (β) energy transfer process is larger than the above (α) direct recombination process, the generation efficiency of the triplet excited state of the guest material 132 can be reduced, and thermal deactivation is reduced. It is preferable because it can be used. For this purpose, the concentration of the guest material 132 with respect to the host material 131 is preferably low.

  Next, the governing factors of the intermolecular energy transfer process between the host material 131 and the guest material 132 will be described. As a mechanism of energy transfer between molecules, two mechanisms, a Forster mechanism (dipole-dipole interaction) and a Dexter mechanism (electron exchange interaction) have been proposed.

<< 1-4. Forster mechanism >>
In the Forster mechanism, energy transfer does not require direct contact between molecules, and energy transfer occurs through a resonance phenomenon of dipole vibration between the host material 131 and the guest material 132. The host material 131 transfers energy to the guest material 132 by the resonance phenomenon of dipole vibration, the excited host material 131 becomes the ground state, and the ground state guest material 132 becomes the excited state. In addition, the rate constant k _{h * → g} of the Forster mechanism is shown in Formula (1).

In Equation (1), ν represents the frequency, and f ′ _h (ν) is the normalized emission spectrum of the host material 131 (fluorescence spectrum, triplet when discussing energy transfer from the singlet excited state). (Phosphorescence spectrum when discussing energy transfer from the excited state), ε _g (ν) represents the molar extinction coefficient of the guest material 132, N represents the Avogadro number, and n represents the refractive index of the medium. , R represents the intermolecular distance between the host material 131 and the guest material 132, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), c represents the speed of light, and φ represents the emission quantum (fluorescence quantum yield in energy transfer from a singlet excited state, phosphorescence quantum yield in energy transfer from a triplet excited state) yields represent, K ^2, the host material 131 and a guest material Coefficient representing the orientation of the transition dipole moment of the 32 is (0-4). In the case of random orientation, K ² = 2/3.

<< 1-5. Dexter Mechanism >>
In the Dexter mechanism, the host material 131 and the guest material 132 approach the effective contact distance that causes orbital overlap, and energy transfer occurs through exchange of electrons between the excited host material 131 and the ground state guest material 132. Note that the speed constant k _{h * → g} of the Dexter mechanism is shown in Equation (2).

In Equation (2), h is a Planck constant, K is a constant having an energy dimension, ν represents a frequency, and f ′ _h (ν) is normalized of the host material 131. It represents the emission spectrum (fluorescence spectrum when discussing energy transfer from singlet excited state, phosphorescence spectrum when discussing energy transfer from triplet excited state), and ε ′ _g (ν) is the normalization of guest material 132 L represents the effective molecular radius, and R represents the intermolecular distance between the host material 131 and the guest material 132.

Here, the energy transfer efficiency phi _ET from host material 131 to the guest material 132 is represented by Equation (3). k _r represents the rate constant of the emission process of the host material 131 (fluorescence when discussing energy transfer from the singlet excited state, phosphorescence when discussing energy transfer from the triplet excited state), and k _n is the host It represents the rate constant of the non-luminous process (thermal deactivation or intersystem crossing) of the material 131, and τ represents the measured lifetime of the host material 131 in the excited state.

From Equation (3), in order to increase the energy transfer efficiency phi _ET is the rate constant of the energy transfer _{k h * → g} increased, the rate constants other competing _{k r + k n (= 1} / τ) relative It can be seen that it should be smaller.

<< 1-6. Concepts for enhancing energy transfer >>
In any of the energy transfer processes of the above general formula (G1) and general formula (G2), the singlet excited state ( ¹ H ^* ) of the host material 131 changes to the singlet excited state ( ¹ G ^* ) of the guest material 132. Therefore, energy transfer occurs by both the Förster mechanism (Formula (1)) and the Dexter mechanism (Formula (2)).

First, consider energy transfer by the Förster mechanism. When τ is eliminated from Equation (1) and Equation (3), the energy transfer efficiency _φET has a higher quantum yield φ (fluorescence quantum yield since energy transfer from a singlet excited state is discussed). It ’s good. However, in fact, as an even more important factor, the emission spectrum of the host material 131 (fluorescence spectrum since energy transfer from the singlet excited state is discussed) and the absorption spectrum of the guest material 132 (from the singlet ground state to the singlet excited state). It is preferable that there is a large overlap with the absorption corresponding to the transition. Note that the guest material 132 preferably has a higher molar extinction coefficient. This means that the emission spectrum of the host material 131 and the absorption band appearing on the longest wavelength side of the guest material 132 overlap.

Next, energy transfer by the Dexter mechanism is considered. According to Equation (2), in order to increase the rate constant k _{h * → g} , the emission spectrum of the host material 131 (fluorescence spectrum since energy transfer from the singlet excited state is discussed) and the absorption spectrum of the guest material 132 It can be seen that the larger the overlap with (absorption corresponding to the transition from the singlet ground state to the singlet excited state) is better.

  From the above, optimization of energy transfer efficiency is realized by overlapping of the emission spectrum of the host material 131 and the absorption band appearing on the longest wavelength side of the guest material 132.

Thus, one embodiment of the present invention provides a light-emitting element using a host material 131 having a function as an energy donor capable of efficiently transferring energy to a guest material 132. The host material 131 is characterized in that the singlet excitation energy level and the triplet excitation energy level are close to each other. Specifically, the difference between the lowest excited singlet energy level (S _H ) and the lowest excited triplet energy level (T _H ) of the host material 131 is preferably more than 0 eV and 0.2 eV or less. With the above structure, transition (reverse intersystem crossing) from the lowest excited triplet state to the lowest excited singlet excited state of the host material 131 easily occurs. Therefore, the generation efficiency of the singlet excited state of the host material 131 can be increased. Further, in order to facilitate energy transfer from the singlet excited state of the host material 131 to the singlet excited state of the guest material 132 serving as an energy acceptor, an emission spectrum of the host material 131 (here, thermal activation delay) The emission spectrum of the substance having a function of exhibiting fluorescence) and the absorption band appearing on the longest wavelength side of the guest material 132 are preferably overlapped. By doing so, the generation efficiency of the singlet excited state of the guest material 132 can be increased.

<< 1-7. Concept for controlling energy transfer >>
On the other hand, in order for triplet excitation energy of the host material 131 to be efficiently converted to singlet excitation energy by reverse intersystem crossing, the triplet excitation energy of the host material 131 does not undergo reverse intersystem crossing and the guest material. It is important to suppress the movement to 132. That is, it is important to suppress the energy transfer process from the triplet excitation energy level of the host material 131 to the triplet excitation energy level of the guest material 132.

  The energy transfer process from the triplet excited state of the host material 131 to the triplet excited state of the guest material 132 is energy transfer by a Dexter mechanism (Formula (2)). In order to suppress the energy transfer process by the Dexter mechanism, the emission spectrum (standardized phosphorescence spectrum) of the host material 131 from the standardized triplet excited state and the standardized triplet excitation of the guest material 132 are used. The one where the overlap with the absorption spectrum to a state is smaller is preferable. For this purpose, the energy difference between the triplet excitation energy level of the host material 131 and the triplet excitation energy level of the guest material 132 is preferably large.

When the host material 131 is a thermally activated delayed phosphor, the lowest excited triplet energy level (T _H ) of the host material 131 is close to the lowest excited singlet energy level (S _H ), and the triplet. Since the excitation energy is converted into singlet excitation energy, it may be difficult to observe light emission from the lowest excited triplet energy level ( _TH ), that is, a phosphorescence spectrum. In that case, the lowest excited triplet energy level (T _H) of the host material 131 may be estimated from emission energy of the heat activated delayed fluorescence.

In addition, the absorption spectrum when the guest material 132 transitions from the singlet ground state to the lowest excited triplet state is difficult to observe because the transition is forbidden. Therefore, the lowest excited triplet energy level (T _1G ) of the guest material 132 may be estimated from the emission energy of the phosphorescence spectrum of the guest material 132.

In addition, the emission spectrum (phosphorescence spectrum or thermally activated delayed fluorescence) from the triplet excitation energy level of the normalized host material 131 and the absorption spectrum (or phosphorescence spectrum of the normalized guest material 132 to the triplet excitation energy) (or In order to reduce the overlap with the phosphorescence spectrum of the guest material 132, the lowest excited triplet energy level (T _H ) of the host material 131 is the lowest excited triplet energy level (T _1G ) of the guest material 132. As described above, it is preferable that the energy difference between the energy levels is large. At this time, since the lowest excited singlet energy level (S _H ) of the host material 131 is higher than the lowest excited triplet energy level (T _H ) of the host material 131, the lowest excitation of the guest material 132 is performed. More than triplet energy level (T _1G ). Therefore, it is preferable that the thermally activated delayed fluorescence emission energy of the host material 131 is equal to or greater than the phosphorescence emission energy of the guest material 132 and that the energy difference between the emission energies is large. Specifically, the energy difference between the lowest excited triplet energy level (T _H ) of the host material 131 and the lowest excited triplet energy level (T _1G ) of the guest material 132 is preferably 0.5 eV or more. More preferably, it is 1.0 eV or more. The energy difference between the thermally activated delayed fluorescence emission energy of the host material 131 and the phosphorescence emission energy of the guest material 132 is preferably 0.5 eV or more, and more preferably 1.0 eV or more. Is preferred.

Note that, among the triplet excitation energy levels of the guest material 132, the second excitation triplet energy level (T _2G ) having energy higher than the lowest excitation triplet energy level (T _1G ) is the lowest excitation singlet energy. When the level is lower than the level (S _1G ), the energy difference between the second excited triplet energy level (T _2G ) of the guest material 132 and the lowest excited triplet energy level (T _H ) of the host material 131 is small. Become. Further, the lowest excited triplet energy level of the host material 131 (T _H) is, if it has a second excitation energy above the triplet energy level (T _2G) of the guest material 132, triplet excitation energy of the host material 131 Is from the lowest excited triplet energy level (T _H ) of the host material 131 to the second excited triplet energy level (T _2G ) of the guest material 132, as indicated by route E ₃ in FIG. Energy transfer becomes easier. That is, the probability of generating triplet excited states in the guest material 132 is improved, and the number of excited states that are thermally deactivated increases. Therefore, the reverse intersystem crossing of the route A ₁ and the subsequent energy transfer process shown in the route E ₁ are less likely to occur, and the generation efficiency of the singlet excited state of the guest material 132 is reduced. In other words, it is possible to better energy transfer process shown in Route E ₃ shown in FIG. 1 (C) is small, it is possible to reduce the production efficiency of the triplet excited state of the guest material 132, which reduces the thermal inactivation, preferable.

In order to suppress the energy transfer process, it is preferable that the second excited triplet energy level (T _2G ) of the guest material 132 be equal to or higher than the lowest excited singlet energy level of the guest material 132.

In addition, the second excited triplet energy level (T _2G ) of the guest material 132 is _{equal to} or higher than the lowest excited triplet energy level (T _H ) of the host material 131 and the lowest excited triplet energy level of the host material 131. (T _H ) is preferably _{equal to} or higher than the lowest excited triplet energy level (T _1G ) of the guest material 132.

Furthermore, in order to suppress the energy transfer process indicated by the route E ₃ in FIG. 1C and efficiently generate the reverse intersystem crossing of the route A ₁ and the subsequent energy transfer process indicated by the route E ₁ , the guest material 132 is used. The second excited triplet energy level (T _2G ) is _{equal to} or higher than the lowest excited triplet energy level (T _H ) of the host material 131, and the lowest excited triplet energy level (T _H ) of the host material 131 is More preferably, it is at least the excited singlet energy level (S _1G ) of the guest material 132. In addition, when the host material 131 is a thermally activated delayed phosphor, the lowest excited singlet energy level (S _H ) of the host material 131 is equal to or higher than the lowest excited triplet energy level (T _H ) of the host material 131. Since it is energy, it is _{equal to} or higher than the lowest excited singlet energy level (S _1G ) of the guest material 132. That is, the heat activation delayed fluorescence emission energy of the host material 131 is preferably equal to or higher than the fluorescence emission energy of the guest material 132.

Further, the second excited triplet energy level (T _2G ) of the guest material 132 is more preferably equal to or higher than the lowest excited singlet energy level (S _H ) of the host material 131. At this time, since the lowest excited triplet energy level ( _TH ) of the host material 131 is lower than the lowest excited singlet energy level ( _SH ) of the host material 131, the lowest excited triplet of the host material 131 is present. Energy transfer from the energy level (T _H ) to the second excited triplet energy level (T _2G ) of the guest material 132 can be effectively suppressed. As a result, the generation efficiency of the singlet excited state of the guest material 132 can be improved, and the light emission efficiency of the light emitting element can be improved.

<< 1-8. Material >>
In the light-emitting layer 130, the guest material 132 having the above energy level includes one or more skeletons selected from anthracene, tetracene, chrysene, pyrene, perylene, and acridone, an aromatic amine, an alkyl group, and an aryl group. And a material having one or more substituents selected from among them. In addition, since the skeleton and the substituent are bonded, the lowest excited singlet energy level is stabilized, and the second excited triplet energy level is likely to be equal to or higher than the lowest excited singlet energy level. . In addition, by combining the two substituents having the same structure and the skeleton, the lowest excited singlet energy level is stabilized, and the second excited triplet energy level is equal to or higher than the lowest excited singlet energy level. It is preferable because An organic material having the skeleton is suitable for a light-emitting material because of high fluorescence quantum yield. An organic material having the skeleton is preferable for a light-emitting material because of its high reliability.

  As the aromatic amine which is an example of the substituent that the guest material 132 has, a so-called tertiary amine having no NH group is preferable, and an arylamine skeleton is particularly preferable. The aryl group of the aryl skeleton is preferably a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and examples thereof include a phenyl group, a naphthyl group, and a fluorenyl group. Further, the aryl group may have a substituent, and the substituents may be bonded to each other to form a ring. As the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 13 carbon atoms can also be selected as the substituent. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and a fluorenyl group. Moreover, as an example in which the substituents are bonded to each other to form a ring, for example, when the carbon at the 9-position in the fluorene skeleton has two phenyl groups as substituents, the phenyl groups are bonded to each other, so The case where a skeleton is formed is mentioned. In the case of no substitution, it is advantageous in terms of the ease of synthesis and the price of raw materials.

  Further, examples of the substituent that the guest material 132 has include an alkyl group and an aryl group, each having an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a substituent having 6 to 13 carbon atoms. Alternatively, an unsubstituted aryl group can also be selected as a substituent. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and a fluorenyl group. Further, the aryl group may have a substituent, and the substituents may be bonded to each other to form a ring. Examples of the substituent include an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, an aryl group having 6 to 13 carbon atoms, an aromatic amine, or a π-electron rich heteroaromatic group. You can choose. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and a fluorenyl group. As the aromatic amine, a so-called tertiary amine having no NH bond is preferable, and an arylamine skeleton is particularly preferable. The aryl group of the arylamine skeleton is preferably a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and examples thereof include a phenyl group, a naphthyl group, and a fluorenyl group. Further, as the π-electron rich heteroaromatic, a furan skeleton, a thiophene skeleton or a pyrrole skeleton is preferable because it is stable and reliable, and the dibenzofuran skeleton is preferable as the furan skeleton, and the dibenzothiophene skeleton is pyrrole as the thiophene skeleton. As the skeleton, an indole skeleton and a carbazole skeleton are preferable. Further, these π-electron rich heteroaromatics may further have a substituent. In addition, as an example in which the substituents are bonded to each other to form a ring, for example, when the carbon at the 9-position in the fluorene skeleton has two phenyl groups as substituents, the phenyl groups are bonded to each other, thereby spirofluorene The case where a skeleton is formed is mentioned. In the case of no substitution, it is advantageous in terms of the ease of synthesis and the price of raw materials.

  Examples of the alkyl group and the aryl group are groups represented by the following general formulas (R-1) to (R-30). Note that groups that can be used as an alkyl group and an aryl group are not limited thereto.

  Specific examples of the guest material having the above energy level or the above structure include 9,10-diphenylanthracene (abbreviation: DPAnth), 9- [4- (10-phenyl-9-anthryl) phenyl] -9H. -Carbazole (abbreviation: CzPA), N, N, 9-triphenylanthracene-9-amine (abbreviation: DPhAPhA), 9,10-bis (diphenylamino) anthracene (abbreviation: DPhA2A), N, N'-diphenyl- N, N′-bis [4- (9-phenyl-9H-fluoren-9-yl) phenyl] pyrene-1,6-diamine (abbreviation: 1,6FLPAPrn), N, N′-bis (3-methylphenyl) ) -N, N′-bis [3- (9-phenyl-9H-fluoren-9-yl) phenyl] pyrene-1,6-diamine (abbreviation: 1) 6mMemFLPAPrn), 2,5,8,11-tetra (tert-butyl) perylene (abbreviation: TBP), N, N'-diphenylquinacridone (abbreviation: DPQd), 5,6,11,12-tetraphenylnaphthacene ( Common names: rubrene), 6,12-bis (diphenylamino) chrysene (abbreviation: DPhA2C), and the like.

  Table 1 shows the lowest excited singlet energy level, the lowest excited triplet energy level, and the second excited triplet energy level of an example of an organic compound that can be used for the guest material 132. The structures and abbreviations of these organic compounds are shown below.

  In order to obtain the energy levels shown in Table 1, the most stable structure in the singlet ground state of the organic compound was calculated using a density functional method (DFT). Gaussian 09 was used as the quantum chemistry calculation program. 6-311G (d, p) was used as the basis function, and B3LYP was used as the functional. The calculation was performed using a high performance computer (ICE X, manufactured by SGI). Furthermore, the singlet excitation energy level and the triplet excitation energy level were calculated using a time-dependent density functional method (TD-DFT). Note that the total energy of DFT is represented by the sum of potential energy, electrostatic energy between electrons, and exchange correlation energy including all the interactions between kinetic energy of electrons and complex electrons. In DFT, the exchange correlation interaction is approximated by a functional of one electron potential expressed by electron density (meaning a function of a function), and thus the calculation is highly accurate.

The organic compound shown in Table 1 has a second excited triplet energy level equal to or higher than the lowest excited singlet energy level. Accordingly, by using the organic compounds shown in Table 1 as a guest material 132, it is possible to suppress the energy transfer process of the triplet excitation energy shown in route E ₃ in FIG. 1 (C), the inter-inverse term of Route A ₁ The energy transfer process of singlet excitation energy shown in the intersection and the subsequent route E ₁ is likely to occur. Therefore, the generation efficiency of the singlet excited state of the guest material 132 can be improved.

  In the light-emitting layer 130, the host material 131 may be composed of one kind of compound or a plurality of compounds, but the second excited triplet energy level of the guest material 132 is A compound that is higher than or equal to the lowest excited triplet energy level of the material 131 and in which the lowest excited triplet energy level of the host material 131 is equal to or higher than the lowest excited triplet energy level of the guest material 132 is used as the host material 131. It is preferable to use it. For example, when the host material 131 is composed of a kind of compound, the following compounds can be used.

First, fullerenes and derivatives thereof, acridine derivatives such as proflavine, eosin and the like can be mentioned. In addition, metal-containing porphyrins including magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), palladium (Pd), and the like can be given. Examples of the metal-containing porphyrin include a protoporphyrin-tin fluoride complex (SnF ₂ (Proto IX)), a mesoporphyrin-tin fluoride complex (SnF ₂ (Meso IX)) represented by the following structural formula, and hematoporphyrin. - tin fluoride complex _{(SnF 2 (Hemato IX))} , coproporphyrin tetramethyl ester - tin fluoride complex _{(SnF 2 (Copro III-4Me} )), octaethylporphyrin - tin fluoride complex _(SnF 2 _(OEP)) , Etioporphyrin-tin fluoride complex (SnF ₂ (Etio I)), octaethylporphyrin-platinum chloride complex (PtCl ₂ OEP), and the like. The structures and abbreviations of the organic compounds described above are shown below.

  As the host material 131 composed of a kind of compound, 2- (biphenyl-4-yl) -4,6-bis (12-phenylindolo [2,3-a] represented by the following structural formula Carbazol-11-yl) -1,3,5-triazine (abbreviation: PIC-TRZ), 2,-{4- [3- (N-phenyl-9H-carbazol-3-yl) -9H-carbazole-9 -Yl] phenyl} -4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn), 2- [4- (10H-phenoxazin-10-yl) phenyl] -4,6-diphenyl-1 , 3,5-triazine (abbreviation: PXZ-TRZ), 3- [4- (5-phenyl-5,10-dihydrophenazin-10-yl) phenyl] -4,5-diphenyl-1,2,4- Triazole Abbreviations: PPZ-3TPT), 3- (9,9-dimethyl-9H-acridin-10-yl) -9H-xanthen-9-one (abbreviation: ACRXTN), bis [4- (9,9-dimethyl-9) , 10-dihydroacridine) phenyl] sulfone (abbreviation: DMAC-DPS), 10-phenyl-10H, 10′H-spiro [acridine-9,9′-anthracene] -10′-one (abbreviation: ACRSA), etc. A heterocyclic compound having a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring can also be used. Since the heterocyclic compound has a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring, it is preferable because of its high electron transporting property and hole transporting property. A substance in which a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring are directly bonded has both a donor property of a π-electron rich heteroaromatic ring and an acceptor property of a π-electron deficient heteroaromatic ring, This is particularly preferable because the difference between the energy level in the singlet excited state and the energy level in the triplet excited state is small.

  Table 2 shows the lowest excited singlet energy level and the lowest excited triplet energy level of an example of an organic compound that can be used for the host material 131. The structures and abbreviations of these organic compounds are shown below.

The energy levels shown in Table 2 were calculated using the same calculation method as in Table 1. In the light-emitting element of one embodiment of the present invention, as an example, the second excited triplet energy level of the guest material 132 is selected from the organic compounds shown in Table 2 and the organic compounds shown in Table 1. The host material 131 has a lowest excited triplet energy level of the host material 131 and the lowest excited triplet energy level of the host material 131 becomes equal to or higher than the lowest excited triplet energy level of the guest material 132. And the guest material 132 are preferable. By doing so, the energy transfer process of the triplet excitation energy shown in the route E ₃ in FIG. 1C can be suppressed, and the reverse intersystem crossing of the route A ₁ and the subsequent singlet excitation shown in the route E _1. The energy transfer process of energy is likely to occur. Therefore, the generation efficiency of the singlet excited state of the guest material 132 can be improved.

  In any of the organic compounds shown in Table 2, the energy difference between the lowest excited singlet energy level and the lowest excited triplet excited energy level exceeds 0 eV and is 0.2 eV or less. Therefore, these organic compounds are compounds that can exhibit thermally activated delayed fluorescence at room temperature.

  Here, as an example, transient fluorescence characteristics were measured for PCCzPTzn by time-resolved luminescence measurement.

  The time-resolved luminescence measurement was performed using a thin film sample in which PCCzPTzn was deposited on a quartz substrate so as to have a thickness of 50 nm.

  For the measurement, a picosecond fluorescence lifetime measurement system (manufactured by Hamamatsu Photonics) was used. In this measurement, in order to measure the lifetime of the fluorescence emission exhibited by the thin film, the thin film was irradiated with a pulse laser, and the light emission attenuated after the laser irradiation was time-resolved measured with a streak camera. A nitrogen gas laser having a wavelength of 337 nm was used as the pulse laser, and the thin film was irradiated with a 500 ps pulse laser at a period of 10 Hz, and the data repeatedly measured were integrated to obtain data with a high S / N ratio. Moreover, the measurement was performed at room temperature (atmosphere kept at 23 ° C.).

  FIG. 2 shows the transient fluorescence characteristics of PCCzPTzn obtained by the measurement.

  Further, the attenuation curve shown in FIG. 2 was fitted using the following formula (4).

  In Formula (4), L represents the normalized emission intensity, and t represents the elapsed time. As a result of fitting the attenuation curve, it was possible to perform fitting with n of 1 to 3. From the results of the attenuation curve fitting, it was found that the light emitting component of the PCCzPTzn thin film sample contained a fluorescent component with a fluorescence lifetime of 0.015 μs and a delayed fluorescent component with 1.5 μs. That is, it can be said that PCCzPTzn is a thermally activated delayed phosphor that exhibits delayed fluorescence at room temperature.

  As described above, in the light-emitting element of one embodiment of the present invention, the singlet excitation energy level and the triplet energy level of the guest material 132 and the host material 131 in the light-emitting layer 130 have the above structure, whereby light emission A highly efficient light-emitting element can be provided.

  Note that the light-emitting layer 130 can be formed by a method such as a vapor deposition method (including a vacuum vapor deposition method), an inkjet method, a coating method, or gravure printing.

<2. Configuration Example 2 of Light-Emitting Element>
Next, a structure different from the structures illustrated in FIGS. 1B and 1C will be described below with reference to FIGS.

  FIG. 3A is a schematic cross-sectional view illustrating an example of the light-emitting layer 130 illustrated in FIG. A light-emitting layer 130 illustrated in FIG. 3A includes a host material 131 and a guest material 132, and the host material 131 includes an organic compound 131_1 and an organic compound 131_2.

  The organic compound 131_1 and the organic compound 131_2 are preferably a combination that forms an exciplex. The exciplex has the property that the difference between the singlet excited energy level and the triplet excited energy level tends to be very small, so the transition from the triplet excited state to the singlet excited state (between inverse terms) Crossing) is likely to occur.

Note that even when the host material 131 is used so that the organic compound 131_1 and the organic compound 131_2 form a combination that forms an exciplex, light emission from the guest material 132 can be obtained by the following two processes. .
(Α) Direct recombination process (β) Energy transfer process

  The (α) direct recombination process is as described in 1-2. Since this is the same as the process described in, description is omitted here.

<< 2-1. (Β) Luminescence mechanism through energy transfer process »
The combination of the organic compound 131_1 that forms the exciplex in the light-emitting layer 130 and the organic compound 131_2 is not particularly limited as long as it is a combination that can form an exciplex, but one of them has a hole transporting property. More preferably, the other is a material having an electron transporting property. In this case, it becomes easy to form a donor-acceptor type excited state, and an excited complex can be formed efficiently. In the case where the combination of the organic compound 131_1 and the organic compound 131_2 is configured by a combination of a material having a hole transporting property and a material having an electron transporting property, the carrier balance can be easily controlled by the mixture ratio. Specifically, a material having a hole transporting property: a material having an electron transporting property = 1: 9 to 9: 1 (weight ratio) is preferable. In addition, since the carrier balance can be easily controlled by having this configuration, the recombination region can be easily controlled.

  The difference between the lowest excited singlet energy level of the exciplex formed by the organic compound 131_1 and the organic compound 131_2 and the lowest excited triplet energy level of the exciplex is more than 0 eV and 0.2 eV or less. And preferred. With the above structure, a transition from the triplet excitation energy level of the exciplex to the singlet excitation energy level (cross-reverse crossing) is likely to occur. Therefore, the generation efficiency of the excited complex, that is, the singlet excited state of the host material 131 can be increased. Note that in order to efficiently generate the crossing between the reverse terms, the triplet excitation energy level of the exciplex is the triplet excitation energy level of each organic compound (organic compound 131_1 and organic compound 131_2) that forms the exciplex. Is preferably lower. Accordingly, quenching of triplet excitation energy of the exciplex by the organic compound 131_1 and the organic compound 131_2 is less likely to occur, and reverse intersystem crossing efficiently occurs.

  Further, the emission spectrum of the host material 131 (here, the emission spectrum of the exciplex formed by the organic compound 131_1 and the organic compound 131_2) overlaps with the absorption band that appears on the longest wavelength side of the guest material 132. preferable. With the above structure, energy transfer from the singlet excited state of the host material 131 to the singlet excited state of the guest material 132 easily occurs. Therefore, the generation efficiency of the singlet excited state of the guest material 132 can be increased, and the light emission efficiency can be increased.

Here, in order to explain the energy transfer process of the exciplex, FIG. 3B is a schematic diagram for explaining the correlation of energy levels. In addition, the notation and code | symbol in FIG. 3 (B) are as follows.
Host1 (131_1): Organic compound 131_1
Host2 (131_2): Organic compound 131_2
Guest (132): Guest material 132 (fluorescent material)
S _H1 : lowest excited singlet energy level of the organic compound 131_1 T _H1 : lowest excited triplet energy level of the organic compound 131_1 S _E : lowest excited singlet energy level of the exciplex T _E : exciplex Lowest excited triplet energy level of S _1G : lowest excited singlet energy level of guest material 132 (fluorescent material) T _1G : lowest excited triplet energy level of guest material 132 (fluorescent material) T _2G : Second excited triplet energy level of guest material 132 (fluorescent material)

  When the carrier is transported to the light-emitting layer 130, one of the organic compound 131_1 and the organic compound 131_2 receives a hole, the other receives an electron, and a cation and an anion are close to each other, so that an exciplex is quickly formed. Alternatively, when one is in an excited state, it rapidly interacts with the other substance to form an exciplex. Therefore, most excitons in the light emitting layer 130 exist as exciplexes. Since the exciplex has a smaller band gap than both the organic compound 131_1 and the organic compound 131_2, the exciplex is formed by recombination of one hole and the other electron, whereby the driving voltage can be reduced.

As shown in FIG. 3B, the organic compound 131_1 and the organic compound 131_2 included in the host material 131 form an exciplex. At this time, since it becomes possible to form a donor-acceptor type excited state, the S _E of the exciplex and the T _E of the exciplex are close to each other.

When the excited state of the exciplex is a singlet excited state and the S _{E of the} exciplex is equal to or higher than S _{1G of} the guest material, as shown in the route E ₄ in FIG. Excitation energy is transferred from _E to S _1G of the guest material 132, and the guest material 132 is in a singlet excited state. Fluorescence emission is obtained from the guest material 132 in a singlet excited state. That is, energy transfer from the singlet excited state of the exciplex to the singlet excited state of the guest material 132 occurs as shown in the following general formula (G3).

¹ [HA] ^* + ¹ G → ¹ H + ¹ A + ¹ G ^* (G3)

Note that in General Formula (G3), ¹ [HA] ^* represents the lowest excited singlet state of an exciplex formed of the organic compound 131_1 and the organic compound 131_2, and ¹ G represents a singlet base of the guest material 132 ¹ H represents the singlet ground state of the organic compound 131_1, ¹ A represents the singlet ground state of the organic compound 131_2, and ¹ G ^* represents the lowest excited singlet state of the guest material 132.

Therefore, when the excited state of the exciplex functioning as the host material 131 is a singlet excited state, the lowest excited singlet energy level (S _E ) of the exciplex is the lowest excited singlet energy level of the guest material 132 ( S _1G ) or more is preferable.

  Next, when the organic compound 131_1 and the organic compound 131_2 form an exciplex and is in a triplet excited state, fluorescence emission is obtained by following the following two processes.

The exciplex has a function of converting a part of triplet excitation energy into singlet excitation energy by reverse intersystem crossing. Therefore, as a first process, first, a route A ₂ in FIG. as shown, the reverse intersystem crossing from T _E of the exciplex (upconversion), excitation energy into S _E moves.

As the second step subsequent, _{S E} of the exciplex, is equal to or greater than _{S 1G} of the guest material 132, as shown in route _{E 4} in FIG. 3 (B), the guest material 132 from _{S E} exciplex Excitation energy is transferred to S _{1G of} , and the guest material 132 is in a singlet excited state. Fluorescence emission is obtained from the guest material 132 in a singlet excited state.

Note that the process of the route A ₂ and the route E ₄ described above may be referred to as ExSET (Exciplex-Single Energy Transfer) or ExEF (Exciplex-Enhanced Fluorescence) in this specification and the like.

  The first process and the second process are represented by the following general formula (G4).

^{3 [H-A] * +} 1 G → ( reverse intersystem ^{crossing) → 1 [H-A]} * + 1 G → 1 H + 1 A + 1 G * (G4)

Note that in General Formula (G4), ³ [HA] ^* represents the lowest excited triplet state of an exciplex formed of the organic compound 131_1 and the organic compound 131_2, and ¹ G represents a singlet base of the guest material 132. represents the ^state, 1 ^{[H-a] *} represents a lowest excited singlet state of the exciplex formed by the organic compound 131_1 and the organic compound ^{131_2, 1} H represents the singlet ground state of an organic compound ^{131_1, 1} A represents the singlet ground state of the organic compound 131_2, and ¹ G ^* represents the lowest excited singlet state of the guest material 132.

As shown in the general formula (G4), the lowest excited triplet state of the exciplex ^{(3 [H-A] *} ) by reverse intersystem crossing from the lowest excited singlet state of the exciplex ^{(1 [H-A] *} ) And then the excitation energy is transferred to the lowest excited singlet state ( ¹ G ^* ) of the guest material 132.

  When the host material 131 has the above-described configuration, the (β) energy transfer process is efficiently generated, and both the singlet excitation energy and the triplet excitation energy of the exciplex are efficiently singlet excited state of the guest material 132. Therefore, light emission from the guest material 132 (fluorescent material) of the light emitting layer 130 can be efficiently obtained.

However, before the excitation energy is transferred from the exciplex to the guest material 132, if the exciplex is deactivated by emitting the excitation energy as light or heat, the light emission efficiency is lowered. Furthermore, it as previous processes, the efficiency of the process of A ₂ which intersects between Gyakuko the singlet excited state from a triplet excited state in the exciplex falls, also the luminous efficiency is lowered. In particular, when T _{E of} the exciplex is lower than T _{1G of the} guest material 132, S _E ≧ S _1G > T _1G > T _E , so that the energy difference between T _E and S _E becomes large. As a result, the reverse intersystem crossing of the route A ₂ in FIG. 3B and the subsequent energy transfer process shown in the route E ₄ are less likely to occur, and the generation efficiency of the singlet excited state of the guest material 132 is reduced. Therefore, the lowest excited triplet energy level (T _E ) of the exciplex is preferably _{equal to} or higher than the lowest excited triplet energy level (T _1G ) of the guest material 132. Further, it is more preferable that the energy difference between these energy levels is larger. Specifically, the energy difference between the lowest excited triplet energy level (T _E ) of the exciplex and the lowest excited triplet energy level (T _1G ) of the guest material 132 is preferably 0.5 eV or more, More preferably, it is 1.0 eV or more.

At this time, when the exciplex shows thermally activated delayed fluorescence, the lowest excited singlet energy level (S _E ) of the exciplex is higher than the lowest excited triplet energy level (T _E ) of the exciplex. _Therefore, it becomes higher than the lowest excited triplet energy level (T _1G ) of the guest material 132. That is, it is preferable that the emission energy of the thermally activated delayed fluorescence of the exciplex is equal to or higher than the phosphorescence emission energy of the guest material 132. Further, it is more preferable that the energy difference between these energy levels is larger. Specifically, the energy difference between the thermally activated delayed fluorescence emission energy of the exciplex and the phosphorescence emission energy of the guest material 132 is preferably 0.5 eV or more, more preferably 1.0 eV or more.

At this time, as shown in route _{E 5} in FIG. 3 (B), even if the excitation energy _{T 1G} of the guest material 132 from _{T E} of the exciplex is moved to thermal inactivation. Therefore, it is less energy transfer shown in route E ₅ shown in FIG. 3 (B) is, it is possible to reduce the production efficiency of the triplet excited state of the guest material 132, it is possible to reduce heat-inactivated, preferably . For this purpose, the concentration of the guest material 132 with respect to the host material 131 is preferably low.

When the second excited triplet energy level (T _2G ) having energy higher than the lowest excited triplet energy level (T _1G ) among the triplet excited energy levels of the guest material 132 is lower than S _1G , as shown in route _{E 6} in FIG. 3 (B), part of the excitation from _{T E} of the exciplex to _{T 2G} of the guest material 132 energy is likely to move. The guest material 132 does not contribute to light emission because it is thermally deactivated even in the second excited triplet state.

Note that in the case where excitation energy is transferred from the exciplex to the guest material 132, energy transfer is easier when the energy difference between the energy levels is smaller. That is, when T _{2G of the} guest material 132 is higher than T _{1G and} lower than S _1G , the second excited state of the guest material 132 from the lowest excited triplet energy level (T _E ) of the exciplex is shown as shown in the route E ₆ . Energy transfer to the excited triplet energy level (T _2G ) is likely to occur, and the generation probability of the triplet excited state of the guest material 132 is improved. Therefore, the reverse intersystem crossing of route A ₂ and the subsequent energy transfer process shown in route E ₄ are less likely to occur, and the generation efficiency of the singlet excited state of guest material 132 is reduced. In other words, it is possible to it is less energy transfer process shown in Route E ₆ shown in FIG. 3 (B) is, it is possible to reduce the production efficiency of the triplet excited state of the guest material 132, which reduces the thermal inactivation, preferable.

Therefore, in order to suppress the energy transfer process illustrated in the route E ₆ in FIG. 3B, the second excited triplet energy level (T _2G ) of the guest material 132 is set to be the lowest excited singlet energy of the guest material 132. It is preferable that it is more than a level ( _S1G ).

The second excited triplet energy level (T _2G ) of the guest material 132 is _{equal to} or higher than the lowest excited triplet energy level (T _E ) of the exciplex, and the lowest excited triplet energy level (T _E ) of the exciplex. _E ) is preferably _{equal to} or higher than the lowest excited triplet energy level (T _1G ) of the guest material 132.

Further, in order to suppress the energy transfer process indicated by the route E ₆ in FIG. 3B and efficiently generate the reverse intersystem crossing of the route A ₂ and the subsequent energy transfer process indicated by the route E ₄ , the guest material 132 is used. the second excited triplet energy level (T _2G) is a pumping lowest excited triplet energy level (T _E) of the complex above, the lowest excited triplet energy level of the exciplex (T _E), the guest It is more preferable that the energy is not lower than the lowest excited singlet energy level (S _1G ) of the material 132. At this time, since the lowest excited singlet energy level (S _E ) of the exciplex is higher than the lowest excited triplet energy level (T _E ) of the exciplex, the lowest excited singlet of the guest material 132 It becomes energy level (S _1G ) or more. That is, when the exciplex exhibits thermally activated delayed fluorescence, the emission energy of the thermally activated delayed fluorescence of the exciplex is preferably greater than or equal to the fluorescence emission energy of the guest material 132.

The second excited triplet energy level (T _2G ) of the guest material 132 is more preferably equal to or higher than the lowest excited singlet energy level (S _E ) of the exciplex. At this time, the lowest excited triplet energy level (T _E ) of the exciplex is lower than the lowest excited singlet energy level (S _E ) of the exciplex, and therefore the lowest excited triplet energy level of the exciplex. Energy transfer from (T _E ) to the second excited triplet energy level (T _2G ) of the guest material 132 can be effectively suppressed. As a result, the generation efficiency of the singlet excited state of the guest material 132 can be improved, and the light emission efficiency of the light emitting element can be improved.

  Note that when the direct recombination process in the guest material 132 becomes dominant, a large number of triplet excited states of the guest material 132 are generated in the light emitting layer, and the light emission efficiency is deteriorated due to thermal deactivation. That is, when the ratio of the (β) energy transfer process is larger than the above (α) direct recombination process, the generation efficiency of the triplet excited state of the guest material 132 can be reduced and thermal deactivation is reduced. It is preferable because it can be used. For that purpose, the concentration of the guest material 132 with respect to the organic compound 131_1 and the organic compound 131_2 is preferably lower.

<< 2-2. Material >>
In the light-emitting layer 130, when the host material 131 is formed of the organic compound 131_1 and the organic compound 131_2, that is, the host material is formed of two kinds of materials, for example, the following materials can be used.

  Note that as the organic compound 131_1 and the organic compound 131_2, it is preferable to use two types of organic compounds that form an exciplex. In this case, various organic compounds can be used as appropriate. However, in order to efficiently form an exciplex, a compound that easily receives electrons (a material having an electron transporting property) and a compound that easily receives holes (hole transport) It is particularly preferable to combine it with a material having properties.

  This is because when a material having an electron transporting property and a material having a hole transporting property are combined to form a host material that forms an exciplex, the mixing ratio of the material having the electron transporting property and the material having the hole transporting property is By adjusting, it becomes easy to optimize the carrier balance of holes and electrons in the light emitting layer. By optimizing the carrier balance between holes and electrons in the light emitting layer, it is possible to suppress the bias of the region where recombination of electrons and holes occurs in the light emitting layer. By suppressing the bias of the region where recombination occurs, the reliability of the light-emitting element can be improved.

  As a compound that easily accepts electrons (a material having an electron transporting property), a π-electron deficient heteroaromatic, a metal complex, or the like can be used. Specifically, bis (10-hydroxybenzo [h] quinolinato) beryllium (II) (abbreviation: BeBq2), bis (2-methyl-8-quinolinolato) (4-phenylphenolato) aluminum (III) (abbreviation: BAlq), bis (8-quinolinolato) zinc (II) (abbreviation: Znq), bis [2- (2-benzoxazolyl) phenolato] zinc (II) (abbreviation: ZnPBO), bis [2- (2- Benzothiazolyl) phenolato] zinc (II) (abbreviation: ZnBTZ) or a metal complex such as 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (abbreviation: PBD), 3- (4-biphenylyl) -4-phenyl-5- (4-tert-butylphenyl) -1,2,4-triazole (abbreviation: TAZ), 9 [4- (4,5-diphenyl-4H-1,2,4-triazol-3-yl) phenyl] -9H-carbazole (abbreviation: CzTAZ1), 1,3-bis [5- (p-tert-butyl) Phenyl) -1,3,4-oxadiazol-2-yl] benzene (abbreviation: OXD-7), 9- [4- (5-phenyl-1,3,4-oxadiazol-2-yl) Phenyl] -9H-carbazole (abbreviation: CO11), 2,2 ′, 2 ″-(1,3,5-benzenetriyl) tris (1-phenyl-1H-benzimidazole) (abbreviation: TPBI), 2 A heterocyclic compound having an azole skeleton such as-[3- (dibenzothiophen-4-yl) phenyl] -1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II), and 2- [3- (dibenzo Ofen-4-yl) phenyl] dibenzo [f, h] quinoxaline (abbreviation: 2mDBTPDBq-II), 2- [3 ′-(dibenzothiophen-4-yl) biphenyl-3-yl] dibenzo [f, h] quinoxaline (Abbreviation: 2mDBTBPDBq-II), 2- [3 ′-(9H-carbazol-9-yl) biphenyl-3-yl] dibenzo [f, h] quinoxaline (abbreviation: 2mCzBPDBq), 2- [3- {3- (9H-carbazol-9-yl) -9H-carbazol-9-yl} -phenyl] dibenzo [f, h] quinoxaline (abbreviation: 2mCzCzPDBq), 4,6-bis [3- (9H-carbazol-9-yl) ) Phenyl] pyrimidine (abbreviation: 4,6mCzP2Pm), 4,6-bis [3- (phenanthren-9-yl) phenyl ] Heterocyclic compounds having a diazine skeleton such as pyrimidine (abbreviation: 4,6mPnP2Pm), 4,6-bis [3- (4-dibenzothienyl) phenyl] pyrimidine (abbreviation: 4,6mDBTP2Pm-II), and PCCzPTzn Heterocyclic compounds having a triazine skeleton, 3,5-bis [3- (9H-carbazol-9-yl) phenyl] pyridine (abbreviation: 35DCzPPy), 1,3,5-tri [3- (3-pyridyl) And heterocyclic compounds having a pyridine skeleton such as phenyl] benzene (abbreviation: TmPyPB). Among the compounds described above, a heterocyclic compound having a diazine skeleton and a triazine skeleton and a heterocyclic compound having a pyridine skeleton are preferable because they have good reliability. In particular, a heterocyclic compound having a diazine (pyrimidine or pyrazine) skeleton and a triazine skeleton has a high electron transport property and contributes to a reduction in driving voltage.

  As a compound that easily receives holes (a material having a hole transporting property), a π-electron rich heteroaromatic or aromatic amine can be preferably used. Specifically, 2- [N- (9-phenylcarbazol-3-yl) -N-phenylamino] spiro-9,9′-bifluorene (abbreviation: PCASF), 4,4′-bis [N- ( 1-naphthyl) -N-phenylamino] biphenyl (abbreviation: NPB), N, N′-bis (3-methylphenyl) -N, N′-diphenyl- [1,1′-biphenyl] -4,4 ′ -Diamine (abbreviation: TPD), 4,4'-bis [N- (spiro-9,9'-bifluoren-2-yl) -N-phenylamino] biphenyl (abbreviation: BSPB), 4-phenyl-4 ' -(9-phenylfluoren-9-yl) triphenylamine (abbreviation: BPAFLP), 4-phenyl-3 '-(9-phenylfluoren-9-yl) triphenylamine (abbreviation: mBPAFLP), 4-pheni -4 ′-(9-phenyl-9H-carbazol-3-yl) triphenylamine (abbreviation: PCBA1BP), 4,4′-diphenyl-4 ″-(9-phenyl-9H-carbazol-3-yl) Triphenylamine (abbreviation: PCBBi1BP), 4- (1-naphthyl) -4 ′-(9-phenyl-9H-carbazol-3-yl) triphenylamine (abbreviation: PCBBANB), 4,4′-di (1 -Naphthyl) -4 ''-(9-phenyl-9H-carbazol-3-yl) triphenylamine (abbreviation: PCBNBB), 9,9-dimethyl-N-phenyl-N- [4- (9-phenyl- 9H-carbazol-3-yl) phenyl] -fluoren-2-amine (abbreviation: PCBAF), N-phenyl-N- [4- (9-phenyl-9H-carbazole) 3-yl) phenyl] -spiro-9,9'-bifluoren-2-amine (abbreviation: PCBASF), N- (1,1'-biphenyl-4-yl) -N- [4- (9-phenyl- 9H-carbazol-3-yl) phenyl] -9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) and other compounds having an aromatic amine skeleton, 1,3-bis (N-carbazolyl) Benzene (abbreviation: mCP), 4,4′-di (N-carbazolyl) biphenyl (abbreviation: CBP), 3,6-bis (3,5-diphenylphenyl) -9-phenylcarbazole (abbreviation: CzTP), 3 , 6-Di (9H-carbazol-9-yl) -9-phenyl-9H-carbazole (abbreviation: PhCzGI), 2,8-di (9H-carbazol-9-yl) -dibenzothio Compounds having a carbazole skeleton such as phen (abbreviation: Cz2DBT), 9-phenyl-9H-3- (9-phenyl-9H-carbazol-3-yl) carbazole (abbreviation: PCCP), and 4,4 ′, 4 ′ '-(Benzene-1,3,5-triyl) tri (dibenzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4- [4- (9-phenyl-9H-fluoren-9-yl) Thiophene skeletons such as phenyl] dibenzothiophene (abbreviation: DBTFLP-III) and 4- [4- (9-phenyl-9H-fluoren-9-yl) phenyl] -6-phenyldibenzothiophene (abbreviation: DBTFLP-IV) And 4,4 ′, 4 ″-(benzene-1,3,5-triyl) tri (dibenzofuran) (abbreviation: DBF3P— I), 4- {3- [3- (9- phenyl--9H- fluoren-9-yl) phenyl] phenyl} dibenzofuran (abbreviation: mmDBFFLBi-II) compound having a furan skeleton such like. Among the compounds described above, a compound having an aromatic amine skeleton and a compound having a carbazole skeleton are preferable because they have good reliability, high hole transportability, and contribute to reduction in driving voltage.

  The organic compound 131_1 and the organic compound 131_2 are not limited to the above-described compounds, and are a combination capable of transporting carriers and forming an exciplex, and the emission of the exciplex is the longest wavelength in the absorption spectrum of the light-emitting substance. As long as it overlaps with the absorption band on the side (absorption corresponding to the transition from the singlet ground state to the singlet excited state of the light-emitting substance), other materials may be used.

  Note that as the material that can be used as the guest material 132 in the light-emitting layer 130 illustrated in FIG. 3A, the second excited triplet energy level of the guest material 132 is the lowest excited singlet energy level of the guest material 132. It is preferable to use a material that is higher than the order.

  In addition, the second excited triplet energy level of the guest material 132 is equal to or higher than the lowest excited triplet energy level of the exciplex, and the lowest excited triplet energy level of the exciplex is equal to the lowest excited triplet energy level of the guest material 132. It is preferable that it is more than an energy level.

  The guest material 132 having the above energy level is selected from one or more skeletons selected from anthracene, tetracene, chrysene, pyrene, perylene, and acridone, and aromatic amines, alkyl groups, and aryl groups. And a material having one or more substituents. In addition, since the skeleton and the substituent are bonded to each other, the lowest excited singlet energy level is lowered, and the second excited triplet energy level is likely to be equal to or higher than the lowest excited singlet energy level. . In addition, by combining the two substituents having the same structure and the skeleton, the lowest excited singlet energy level is lowered, and the second excited triplet energy level is equal to or higher than the lowest excited singlet energy level. It is preferable because An organic compound having the skeleton is suitable for a light-emitting material because of its high fluorescence quantum yield. An organic compound having the skeleton is suitable for a light-emitting material because of its high reliability.

  Note that specific examples of the guest material 132 having the above energy level or the above structure include 1-8. Since this is the same as the guest material 132 shown in FIG.

By using the above energy levels or an organic compound having the above structure, as a guest material 132, it is possible to suppress the energy transfer process of the triplet excitation energy shown in route E ₆ in FIG. 3 (B), the route The energy transfer process of singlet excitation energy shown in the crossing between the reverse terms of A ₂ and the subsequent route E ₄ is likely to occur. Therefore, the generation efficiency of the singlet excited state of the guest material 132 can be improved.

  As described above, in the light-emitting element of one embodiment of the present invention, the singlet excitation energy level and the triplet excitation energy level of the guest material 132 and the host material 131 in the light-emitting layer 130 have the above structure. A light-emitting element with high emission efficiency can be provided.

  Note that the light-emitting layer 130 can be formed by a method such as a vapor deposition method (including a vacuum vapor deposition method), an inkjet method, a coating method, or gravure printing.

<3. Components of light emitting element>
Next, details of other structures of the light-emitting element 150 illustrated in FIG.

<< 3-1. Pair of electrodes >>
The electrode 101 and the electrode 102 have a function of injecting holes and electrons into the light-emitting layer 130. The electrode 101 and the electrode 102 can be formed using a metal, an alloy, a conductive compound, a mixture or a stacked body thereof. Aluminum is a typical example of the metal, and other transition metals such as silver, tungsten, chromium, molybdenum, copper, and titanium, alkali metals such as lithium and cesium, and Group 2 metals such as calcium and magnesium can be used. . A rare earth metal such as ytterbium (Yb) may be used as the transition metal. As the alloy, an alloy containing the above metal can be used, and examples thereof include MgAg and AlLi. Examples of the conductive compound include metal oxides such as indium tin oxide (Indium Tin Oxide). An inorganic carbon-based material such as graphene may be used as the conductive compound. As described above, one or both of the electrode 101 and the electrode 102 may be formed by stacking a plurality of these materials.

  Light emitted from the light-emitting layer 130 is extracted through one or both of the electrode 101 and the electrode 102. Accordingly, at least one of the electrode 101 and the electrode 102 transmits visible light. In the case where a material having low light transmission property such as a metal or an alloy is used for the electrode from which light is extracted, the electrode 101 and the electrode 102 have a thickness that can transmit visible light (for example, 1 nm to 10 nm). One or both may be formed.

<< 3-2. Hole injection layer >>
The hole injection layer 111 has a function of promoting hole injection by reducing a hole injection barrier from the electrode 101, and is formed of, for example, a transition metal oxide, a phthalocyanine derivative, or an aromatic amine. Examples of the transition metal oxide include molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, and manganese oxide. Examples of the phthalocyanine derivative include phthalocyanine and metal phthalocyanine. Examples of aromatic amines include benzidine derivatives and phenylenediamine derivatives. High molecular compounds such as polythiophene and polyaniline can also be used. For example, self-doped polythiophene poly (ethylenedioxythiophene) / poly (styrenesulfonic acid) is a typical example.

As the hole-injecting layer 111, a layer including a composite material of a hole-transporting material and a material that exhibits an electron-accepting property can be used. Alternatively, a stack of a layer containing a material showing an electron accepting property and a layer containing a hole transporting material may be used. Charges can be transferred between these materials in a steady state or in the presence of an electric field. Examples of the material exhibiting electron acceptability include organic acceptors such as quinodimethane derivatives, chloranil derivatives, and hexaazatriphenylene derivatives. Specifically, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F ₄ -TCNQ), chloranil, 2,3,6,7,10,11 -A compound having an electron withdrawing group (halogen group or cyano group) such as hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation: HAT-CN). Transition metal oxides such as Group 4 to Group 8 metal oxides can also be used. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, rhenium oxide, and the like. Among these, molybdenum oxide is preferable because it is stable in the air, has a low hygroscopic property, and is easy to handle.

As the hole transporting material, a material having a hole transporting property higher than that of electrons can be used, and a material having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or more is preferable. Specifically, aromatic amines, carbazole derivatives, aromatic hydrocarbons, stilbene derivatives, and the like can be used. The hole transporting material may be a polymer compound. Alternatively, the hole-transporting material exemplified for the light-emitting layer 130 can be used.

<< 3-3. Hole transport layer >>
The hole transport layer 112 is a layer including a hole transport material, and the materials exemplified as the material of the hole injection layer 111 can be used. Since the hole transport layer 112 has a function of transporting holes injected into the hole injection layer 111 to the light emitting layer 130, the highest occupied orbit of the hole injection layer 111 (also referred to as Highest Occupied Molecular Orbital, HOMO) It is preferable to have the same or close HOMO.

<< 3-4. Electron transport layer >>
The electron transport layer 117 has a function of transporting electrons injected from the electrode 102 through the electron injection layer 118 to the light emitting layer 130. As the electron transporting material, a material having a higher electron transporting property than holes can be used, and a material having an electron mobility of 1 × 10 ⁻⁶ cm ² / Vs or more is preferable. Specific examples include metal complexes having a quinoline ligand, a benzoquinoline ligand, an oxazole ligand, or a thiazole ligand, oxadiazole derivatives, triazole derivatives, phenanthroline derivatives, pyridine derivatives, and bipyridine derivatives. It is done. Alternatively, the electron-transport material exemplified for the light-emitting layer 130 can be used.

<< 3-5. Electron injection layer >>
The electron injection layer 118 has a function of promoting electron injection by reducing an electron injection barrier from the electrode 102. For example, a Group 1 metal, a Group 2 metal, or an oxide, halide, carbonate, or the like thereof. Can be used. Alternatively, a composite material of the electron transporting material described above and a material exhibiting an electron donating property can be used. Examples of the material exhibiting electron donating properties include Group 1 metals, Group 2 metals, and oxides thereof.

  Note that the hole injection layer 111, the hole transport layer 112, the electron transport layer 117, and the electron injection layer 118 described above are formed by an evaporation method (including a vacuum evaporation method), an inkjet method, a coating method, a gravure printing method, and the like, respectively. It can form by the method of.

  In addition to the materials described above, the hole injection layer 111, the hole transport layer 112, the light emitting layer 130, the electron transport layer 117, and the electron injection layer 118 include an inorganic compound or a polymer compound (an oligomer, a dendrimer, a polymer, or the like). ) May be used.

<< 3-6. Substrate >>
The light-emitting element 150 may be manufactured over a substrate made of glass, plastic, or the like. As the order of manufacturing on the substrate, the layers may be sequentially stacked from the electrode 101 side or may be sequentially stacked from the electrode 102 side.

  Note that as the substrate over which the light-emitting element 150 can be formed, glass, quartz, plastic, or the like can be used, for example. A flexible substrate may be used. The flexible substrate is a substrate that can be bent (flexible), and examples thereof include a plastic substrate made of polycarbonate or polyarylate. Moreover, a film, an inorganic vapor deposition film, etc. can also be used. Note that other materials may be used as long as they function as a support in the manufacturing process of the light-emitting element and the optical element. Or what is necessary is just to have a function which protects a light emitting element and an optical element.

  For example, the light-emitting element 150 can be formed using various substrates. The kind of board | substrate is not limited to a specific thing. Examples of the substrate include a semiconductor substrate (for example, a single crystal substrate or a silicon substrate), an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a substrate having stainless steel foil, and a tungsten substrate. , A substrate having a tungsten foil, a flexible substrate, a laminated film, a paper containing a fibrous material, or a base film. Examples of the glass substrate include barium borosilicate glass, aluminoborosilicate glass, and soda lime glass. Examples of the flexible substrate, the laminated film, and the base film include the following. For example, there are plastics represented by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), and polytetrafluoroethylene (PTFE). Another example is a resin such as acrylic. Alternatively, examples include polypropylene, polyester, polyvinyl fluoride, and polyvinyl chloride. As an example, there are polyamide, polyimide, aramid, epoxy, an inorganic vapor deposition film, papers, and the like.

  Alternatively, a flexible substrate may be used as the substrate, and the light-emitting element may be formed directly on the flexible substrate. Alternatively, a separation layer may be provided between the substrate and the light-emitting element. The release layer can be used to separate a part from the substrate after the light emitting element is partially or wholly formed thereon, and to transfer the light emitting element to another substrate. At that time, the light-emitting element can be transferred to a substrate having poor heat resistance or a flexible substrate. Note that, for example, a structure of a laminated structure of an inorganic film of a tungsten film and a silicon oxide film or a structure in which a resin film such as polyimide is formed over a substrate can be used for the above-described release layer.

  That is, a light-emitting element may be formed using a certain substrate, and then the light-emitting element may be transferred to another substrate, and the light-emitting element may be disposed on another substrate. As an example of a substrate to which the light emitting element is transferred, in addition to the above-described substrate, a cellophane substrate, a stone substrate, a wood substrate, a cloth substrate (natural fiber (silk, cotton, hemp), synthetic fiber (nylon, polyurethane, polyester) or There are recycled fibers (including acetate, cupra, rayon, recycled polyester), leather substrates, rubber substrates, and the like. By using these substrates, a light-emitting element that is not easily broken, a light-emitting element with high heat resistance, a light-emitting element that is reduced in weight, or a light-emitting element that is thinned can be obtained.

  Further, for example, a field effect transistor (FET) may be formed over the substrate described above, and the light emitting element 150 may be formed over an electrode electrically connected to the FET. Accordingly, an active matrix display device in which driving of the light emitting element 150 is controlled by the FET can be manufactured.

  Note that one embodiment of the present invention is described in this embodiment. Alternatively, in another embodiment, one embodiment of the present invention will be described. Note that one embodiment of the present invention is not limited thereto. For example, in one embodiment of the present invention, an example in which the second excited triplet energy level of the guest material 132 is equal to or higher than the lowest excited singlet energy level of the guest material 132 has been described. Is not limited to this. Depending on circumstances or circumstances, in one embodiment of the present invention, for example, in the guest material 132, the second excited triplet energy level is not higher than the lowest excited singlet energy level of the guest material 132. Also good. For example, in one embodiment of the present invention, an example in which the second excited triplet energy level of the guest material 132 is equal to or higher than the lowest excited triplet energy level of the host material 131 is described. One embodiment is not limited to this. Depending on circumstances or circumstances, in one embodiment of the present invention, for example, the second excited triplet energy level of the guest material 132 may not be equal to or higher than the lowest excited triplet energy level of the host material 131. Good. Alternatively, for example, in one embodiment of the present invention, the host material 131 is an example of a substance that exhibits thermally activated delayed fluorescence at room temperature; however, in one embodiment of the present invention, for example, the host material 131 is You may have substances other than the substance which shows activated delayed fluorescence. Alternatively, depending on circumstances or circumstances, in one embodiment of the present invention, for example, the host material 131 may not include a substance that exhibits thermally activated delayed fluorescence at room temperature. Alternatively, for example, in one embodiment of the present invention, the guest material 132 includes one or more skeletons selected from anthracene, tetracene, chrysene, pyrene, perylene, and acridone, and an aromatic amine, an alkyl group, and an aryl group. However, one embodiment of the present invention is not limited to this. In some cases, the skeleton or the substituent may not be present.

  As described above, the structure described in this embodiment can be combined as appropriate with any of the other embodiments.

(Embodiment 2)
In this embodiment, a light-emitting element having a structure different from that described in Embodiment 1 and a light-emitting mechanism of the light-emitting element will be described below with reference to FIGS.

<Configuration example of light emitting element>
FIG. 4A is a schematic cross-sectional view of the light-emitting element 450.

  A light-emitting element 450 illustrated in FIG. 4A includes a plurality of light-emitting units (light-emitting units 441 and 442 in FIG. 4A) between a pair of electrodes (an electrode 401 and an electrode 402). One light-emitting unit has a structure similar to that of the EL layer 100 illustrated in FIG. That is, the light-emitting element 150 illustrated in FIG. 1 includes one light-emitting unit, and the light-emitting element 450 includes a plurality of light-emitting units. Note that in the light-emitting element 450, the electrode 401 functions as an anode and the electrode 402 functions as a cathode, which will be described below. However, the structure of the light-emitting element 450 may be reversed.

  In the light-emitting element 450 illustrated in FIG. 4A, a light-emitting unit 441 and a light-emitting unit 442 are stacked, and a charge generation layer 445 is provided between the light-emitting unit 441 and the light-emitting unit 442. Note that the light-emitting unit 441 and the light-emitting unit 442 may have the same configuration or different configurations. For example, the EL layer 100 illustrated in FIG. 1A is preferably used for the light-emitting unit 441, and the light-emitting layer including a phosphorescent material as the light-emitting material is preferably used for the light-emitting unit 442.

  That is, the light emitting element 450 includes a light emitting layer 420 and a light emitting layer 430. In addition to the light-emitting layer 420, the light-emitting unit 441 includes a hole injection layer 411, a hole transport layer 412, an electron transport layer 413, and an electron injection layer 414. In addition to the light-emitting layer 430, the light-emitting unit 442 includes a hole injection layer 415, a hole transport layer 416, an electron transport layer 417, and an electron injection layer 418.

The charge generation layer 445 includes a composite material of an organic material and a material exhibiting electron accepting properties. As the composite material, a composite material that can be used for the hole-injection layer 111 described in Embodiment 1 may be used. As the organic material, various compounds such as aromatic amine compounds, carbazole compounds, aromatic hydrocarbons, and high molecular compounds (oligomers, dendrimers, polymers, and the like) can be used. Note that an organic material having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher is preferably used. However, any other material may be used as long as it has a property of transporting more holes than electrons. A composite material of an organic material and an electron-accepting material is excellent in carrier injecting property and carrier transporting property, so that low voltage driving and low current driving can be realized. Note that when the surface of the light emitting unit on the anode side is in contact with the charge generation layer 445 as in the light emitting unit 442, the charge generation layer 445 also serves as a hole injection layer or a hole transport layer of the light emitting unit. Therefore, it is not necessary to provide a hole injection layer or a hole transport layer in the light emitting unit.

  Note that the charge generation layer 445 may be formed as a stacked structure in which a layer including a composite material of an organic material and an electron-accepting material and a layer formed using another material are combined. For example, a layer including a composite material of an organic material and an electron-accepting material is combined with a layer including one material selected from materials exhibiting electron-donating properties and a material having a high electron-transporting property. May be formed. Alternatively, a layer including a composite material of an organic material and a material exhibiting electron accepting properties may be combined with a layer including a transparent conductive film.

  Note that the charge generation layer 445 sandwiched between the light-emitting units 441 and 442 injects electrons into one light-emitting unit and injects holes into the other light-emitting unit when voltage is applied to the electrodes 401 and 402. Anything to do. For example, in FIG. 4A, when a voltage is applied so that the potential of the electrode 401 is higher than the potential of the electrode 402, the charge generation layer 445 injects electrons into the light-emitting unit 441, and Inject holes into

  In FIG. 4A, the light-emitting element having two light-emitting units is described; however, the same can be applied to a light-emitting element in which three or more light-emitting units are stacked. As shown in the light-emitting element 450, a plurality of light-emitting units are partitioned and arranged between a pair of electrodes by a charge generation layer, thereby enabling high-intensity light emission while maintaining a low current density, and a long-life light-emitting element Can be realized. In addition, a light-emitting element with low power consumption can be realized.

  Note that by applying the structure of the EL layer 100 illustrated in FIG. 1A to at least one of the plurality of units, a light-emitting element with high emission efficiency can be provided.

  In addition, the light-emitting layer 420 includes a host material 421 and a guest material 422. In addition, the light-emitting layer 430 includes a host material 431 and a guest material 432. The host material 421 includes an organic compound 421_1 and an organic compound 421_2. The host material 431 includes an organic compound 431_1 and an organic compound 431_2.

  In this embodiment, the light-emitting layer 420 has a structure similar to that of the light-emitting layer 130 illustrated in FIG. That is, the host material 421, the organic compound 421_1, the organic compound 421_2, and the guest material 422 included in the light-emitting layer 420 correspond to the host material 131, the organic compound 131_1, the organic compound 131_2, and the guest material 132 included in the light-emitting layer 130, respectively. To do. The guest material 432 included in the light-emitting layer 430 will be described below as a phosphorescent material.

  Note that the electrode 401, the electrode 402, the hole injection layers 411 and 415, the hole transport layers 412 and 416, the electron transport layers 413 and 417, and the electron injection layers 414 and 418 are described in Embodiment Mode 1. The electrode 101, the electrode 102, the hole injection layer 111, the hole transport layer 112, the electron transport layer 117, and the electron injection layer 118 have the same functions. Therefore, detailed description thereof is omitted in the present embodiment.

<Light emitting mechanism of the light emitting layer 420>
The light-emitting mechanism of the light-emitting layer 420 is the same as that of the light-emitting layer 130 illustrated in FIG.

<Light emitting mechanism of the light emitting layer 430>
Next, the light emission mechanism of the light emitting layer 430 will be described below.

  The organic compound 431_1 and the organic compound 431_2 included in the light-emitting layer 430 form an exciplex. Here, the organic compound 431_1 is referred to as a host material, and the organic compound 431_2 is referred to as an assist material.

  The combination of the organic compound 431_1 and the organic compound 431_2 that form the exciplex in the light-emitting layer 430 may be a combination that can form an exciplex, but one is a material having a hole-transport property, and the other It is more preferable that is a material having an electron transporting property. Note that the combination of the organic compound 431_1 and the organic compound 431_2 may have a structure similar to that of the organic compound 421_1 and the organic compound 421_2 that form an exciplex in the light-emitting layer 420.

FIG. 4B shows the correlation of energy levels among the organic compound 431_1, the organic compound 431_2, and the guest material 432 in the light-emitting layer 430. In addition, the description and code | symbol in FIG. 4 (B) are as follows.
Host (431_1): Host material (organic compound 431_1)
Assist (431_2): Assist material (organic compound 431_2)
Guest (432): Guest material 432 (phosphorescent material)
· _{S PH:} host material lowest level · _{T PH} of the singlet excited state of (organic compound 431_1): host material lowest level · _{T PG} triplet excited state of the (organic compound 431_1): guest material 432 ( The lowest level of the triplet excited state of the phosphorescent material) S _PE : the lowest level of the singlet excited state of the exciplex • T _PE : the lowest level of the triplet excited state of the exciplex

The lowest level (S _PE ) of the singlet excited state of the exciplex and the lowest level (T _PE ) of the triplet excited state of the exciplex formed by the organic compound 431_1 and the organic compound 431_2 are adjacent to each other. so that (see FIG. 4 (B) refer to _{E 7).}

Then, the energy of both the (S _PE ) and (T _PE ) of the exciplex is moved to the lowest level of the triplet excited state of the guest material 432 (phosphorescent material), and light emission is obtained (FIG. 4B ) see _{E 8).}

Incidentally, the process of _{E 7} and _{E 8} shown above, sometimes referred to as ExTET (Exciplex-Triplet Energy Transfer) In this specification and the like.

  In addition, one of the organic compound 431_1 and the organic compound 431_2 receives a hole, the other receives an electron, and forms an exciplex rapidly when they approach each other. Alternatively, when one is in an excited state, it rapidly interacts with the other substance to form an exciplex. Therefore, most excitons in the light emitting layer 430 exist as exciplexes. Since the exciplex has a smaller band gap than both the organic compound 431_1 and the organic compound 431_2, the exciplex is formed by recombination of one hole and the other electron, whereby the driving voltage can be reduced.

  When the light-emitting layer 430 has the above structure, light emission from the guest material 432 (phosphorescent material) of the light-emitting layer 430 can be efficiently obtained.

  Note that a structure in which light emission from the light-emitting layer 420 has a light emission peak on a shorter wavelength side than light emission from the light-emitting layer 430 is preferable. A light-emitting element using a phosphorescent material that emits light having a short wavelength tends to deteriorate in luminance. Thus, a light emitting element with little luminance deterioration can be provided by using short wavelength light emission from the fluorescent material.

  In addition, by obtaining light with different emission wavelengths in the light-emitting layer 420 and the light-emitting layer 430, a multicolor light-emitting element can be obtained. In this case, since the emission spectrum is light in which emission having different emission peaks is synthesized, it becomes an emission spectrum having at least two maximum values.

  The above configuration is also suitable for obtaining white light emission. White light emission can be obtained by making the light of the light emitting layer 420 and the light emitting layer 430 have complementary colors.

  In addition, by using a plurality of light emitting materials having different light emission wavelengths in one or both of the light emitting layer 420 and the light emitting layer 430, white light emission having high color rendering properties composed of three primary colors or four or more colors can be obtained. it can. In this case, one or both of the light-emitting layer 420 and the light-emitting layer 430 may be further divided into layers, and a different light-emitting material may be included in each of the divided layers.

  Next, materials that can be used for the light-emitting layer 420 and the light-emitting layer 430 are described below.

<Materials that can be used for the light-emitting layer 420>
As a material that can be used for the light-emitting layer 420, a material that can be used for the light-emitting layer 130 described in Embodiment 1 above may be used.

<Materials that can be used for the light-emitting layer 430>
In the light-emitting layer 430, the organic compound 431_1 (host material) is present in the largest amount by weight ratio, and the guest material 432 (phosphorescent material) is dispersed in the organic compound 431_1 (host material).

  As the organic compound 431_1 (host material), in addition to zinc and aluminum-based metal complexes, oxadiazole derivatives, triazole derivatives, benzimidazole derivatives, quinoxaline derivatives, dibenzoquinoxaline derivatives, dibenzothiophene derivatives, dibenzofuran derivatives, pyrimidine derivatives, triazine derivatives Pyridine derivatives, bipyridine derivatives, phenanthroline derivatives and the like. Other examples include aromatic amines and carbazole derivatives. In addition, a material that can be used for the light-emitting layer 130 described in Embodiment 1 (a material having a hole-transport property and a material having an electron-transport property) can be used.

  Examples of the guest material 432 (phosphorescent material) include iridium, rhodium, or platinum-based organometallic complexes, or metal complexes. Among these, organic iridium complexes such as iridium-based orthometal complexes are preferable. Examples of orthometalated ligands include 4H-triazole ligands, 1H-triazole ligands, imidazole ligands, pyridine ligands, pyrimidine ligands, pyrazine ligands, and isoquinoline ligands. Can be mentioned. Examples of the metal complex include a platinum complex having a porphyrin ligand.

  The organic compound 431_2 (assist material) is a combination that can form an exciplex with the organic compound 431_1. In this case, the organic compound 431_1, the organic compound 431_1, and the organic compound so that the emission peak of the exciplex overlaps with the absorption band of the triplet MLCT (Metal to Ligand Charge Transfer) transition of the phosphorescent material, more specifically, the absorption band on the longest wavelength side. It is preferable to select 431_2 and the guest material 432 (phosphorescent material). Thereby, it can be set as the light emitting element which luminous efficiency improved greatly. However, when a thermally activated delayed fluorescent material is used instead of the phosphorescent material, it is preferable that the absorption band on the longest wavelength side is a singlet absorption band. Specifically, materials that can be used for the light-emitting layer 130 described in Embodiment 1 (a material having a hole-transport property and a material having an electron-transport property) can be used.

  The light-emitting material included in the light-emitting layer 430 may be a material that can convert triplet excitation energy into light emission. Examples of the material capable of converting the triplet excitation energy into light emission include a thermally activated delayed fluorescent material in addition to the phosphorescent material. Therefore, the portion described as phosphorescent material may be read as thermally activated delayed fluorescent material. A thermally activated delayed fluorescent material is capable of up-converting a triplet excited state to a singlet excited state with a slight amount of thermal energy (interverse crossing) and efficiently emitting light (fluorescence) from the singlet excited state. It is a common material. As a condition for efficiently obtaining thermally activated delayed fluorescence, the energy difference between the triplet excitation energy level and the singlet excitation energy level is preferably more than 0 eV and not more than 0.2 eV, more preferably more than 0 eV. And 0.1 eV or less.

  Further, there is no limitation on the light emission color of the light emitting material included in the light emitting layer 420 and the light emitting material included in the light emitting layer 430, and they may be the same or different. Since the light emission obtained from each is mixed and taken out of the device, the light emitting device can give white light when, for example, the light emission colors of both are complementary colors. In consideration of the reliability of the light emitting element, the emission peak wavelength of the light emitting material included in the light emitting layer 420 is preferably shorter than that of the light emitting material included in the light emitting layer 430.

  Note that the light-emitting layer 420 and the light-emitting layer 430 can be formed by a method such as an evaporation method (including a vacuum evaporation method), an inkjet method, a coating method, or gravure printing.

  Note that the structure described in this embodiment can be combined as appropriate with any of the structures described in the other embodiments.

(Embodiment 3)
In this embodiment, a light-emitting element having a structure different from those described in Embodiments 1 and 2 will be described below with reference to FIGS.

<Configuration example of light emitting element>
FIG. 5A is a schematic cross-sectional view illustrating a light-emitting element 452 of one embodiment of the present invention.

  The light-emitting element 452 includes a plurality of light-emitting units (in FIG. 5A, the light-emitting unit 446 and the light-emitting unit 447) between the electrode 401 and the electrode 402. One light-emitting unit has a structure similar to that of the EL layer 100 illustrated in FIG. That is, the light-emitting element 150 illustrated in FIG. 1A includes one light-emitting unit, and the light-emitting element 452 includes a plurality of light-emitting units. Note that in this embodiment, the electrode 401 is an anode and the electrode 402 is a cathode, but the structure of the light-emitting element 452 may be reversed.

  5A, a light-emitting unit 446 and a light-emitting unit 447 are stacked, and a charge generation layer 445 is provided between the light-emitting unit 446 and the light-emitting unit 447. Note that the light-emitting unit 446 and the light-emitting unit 447 may have the same configuration or different configurations. For example, it is preferable to use a light-emitting layer including a fluorescent material as the light-emitting material for the light-emitting unit 446 and use the EL layer 100 illustrated in FIG.

  That is, the light-emitting element 452 includes the light-emitting layer 460 and the light-emitting layer 470. In addition to the light-emitting layer 460, the light-emitting unit 446 includes a hole injection layer 411, a hole transport layer 412, an electron transport layer 413, and an electron injection layer 414. In addition to the light-emitting layer 470, the light-emitting unit 447 includes a hole injection layer 415, a hole transport layer 416, an electron transport layer 417, and an electron injection layer 418.

  5A illustrates a light-emitting element having two light-emitting units, the present invention can be similarly applied to a light-emitting element in which three or more light-emitting units are stacked. As shown in the light-emitting element 452, a plurality of light-emitting units are partitioned and arranged between a pair of electrodes by a charge generation layer, thereby enabling high-luminance light emission while maintaining a low current density, and a longer-life light-emitting element Can be realized. In addition, a light-emitting element with low power consumption can be realized.

  Note that by applying the structure of the EL layer 100 illustrated in FIG. 1A to at least one of the plurality of units, a light-emitting element with high emission efficiency can be provided.

  The light-emitting layer 460 includes a host material 461 and a guest material 462. In addition, the light-emitting layer 470 includes a host material 471 and a guest material 472. The host material 471 includes an organic compound 471_1 and an organic compound 471_2.

  In this embodiment, the light-emitting layer 470 has a structure similar to that of the light-emitting layer 130 illustrated in FIG. That is, the host material 471, the organic compound 471_1, the organic compound 471_2, and the guest material 472 included in the light-emitting layer 470 correspond to the host material 131, the organic compound 131_1, the organic compound 131_2, and the guest material 132 included in the light-emitting layer 130, respectively. To do. The guest material 462 included in the light-emitting layer 460 is described below as a fluorescent material.

<Light emitting mechanism of light emitting layer 460>
First, the light emission mechanism of the light emitting layer 460 will be described below.

  In the light-emitting layer 460, an excited state is formed by carrier recombination. Since the host material 461 is present in a large amount as compared with the guest material 462, the excited state exists almost as an excited state of the host material 461. The ratio between the singlet excited state and the triplet excited state (hereinafter, exciton generation probability) generated by carrier recombination is about 1: 3.

  First, the case where the triplet excitation energy level of the host material 461 is higher than the triplet excitation energy level of the guest material 462 will be described below.

  Energy transfer (triplet energy transfer) occurs in the guest material 462 from the triplet excited state of the host material 461. However, since the guest material 462 is a fluorescent material, the triplet excited state does not emit light in the visible light region. Therefore, it is difficult to use the triplet excited state of the host material 461 as light emission. Therefore, when the triplet excitation energy level of the host material 461 is higher than the triplet excitation energy level of the guest material 462, it is difficult to use about 25% of the injected carriers for light emission.

Next, FIG. 5B illustrates the correlation of energy levels between the host material 461 and the guest material 462 in the light-emitting layer 460. In addition, the notation and code | symbol in FIG. 5 (B) are as follows.
Host (461): Host material 461
Guest (462): Guest material 462 (fluorescent material)
S _FH : lowest level of singlet excited state of host material 461 T _FH : lowest level of triplet excited state of host material 461 S _FG : singlet excited state of guest material 462 (fluorescent material) The lowest level of T _FG : the lowest level of the triplet excited state of the guest material 462 (fluorescent material)

As shown in FIG. 5B, the triplet excitation energy level of the guest material 462 (in FIG. 5B, T _FG ) is the triplet excitation energy level of the host material 461 (in FIG. 5B). T _FH ).

Further, as shown in FIG. 5 (B), triplet - triplet annihilation (TTA: Triplet-Triplet Annihilation) (see FIG. 5 (B) _{E 9),} by each other triplet excitons collide, the A part is converted into the lowest level (S _FH ) of the singlet excited state of the host material 461. Energy from the lowest level (S _FH ) of the singlet excited state of the host material 461 to the lowest level (S _FG ) of the singlet excited state of the guest material 462 (fluorescent material) having a lower level than that. movement occurs (see FIG. 5 _(B) refer to _{E 10),} a guest material 462 (fluorescent material) to emit light.

Note that since the triplet excitation energy level of the host material 461 is lower than the triplet excitation energy level of the guest material, T _FG does not deactivate and is transferred to T _FH (see E _{11 in} FIG. 5B). And used for TTA.

  When the light-emitting layer 460 has the above structure, light emission from the guest material 462 of the light-emitting layer 460 can be efficiently obtained.

  Note that by obtaining light with different emission wavelengths in the light-emitting layer 460 and the light-emitting layer 470, a multicolor light-emitting element can be obtained. In this case, since the emission spectrum is light in which emission having different emission peaks is synthesized, it becomes an emission spectrum having at least two maximum values.

  The above configuration is also suitable for obtaining white light emission. White light emission can be obtained by making the light of the light emitting layer 460 and the light emitting layer 470 have complementary colors.

  In addition, by using a plurality of light emitting materials having different light emission wavelengths in one or both of the light emitting layer 460 and the light emitting layer 470, white light emission having high color rendering properties composed of three primary colors or four or more colors can be obtained. it can. In this case, one or both of the light-emitting layer 460 and the light-emitting layer 470 may be further divided into layers, and a different light-emitting material may be included in each divided layer.

<Light emitting mechanism of light emitting layer 470>
The light-emitting mechanism of the light-emitting layer 470 is the same as that of the light-emitting layer 130 illustrated in FIG.

  Next, materials that can be used for the light-emitting layer 460 and the light-emitting layer 470 are described below.

<Materials that can be used for the light-emitting layer 460>
In the light emitting layer 460, the host material 461 is present in the largest amount by weight, and the guest material 462 (fluorescent material) is dispersed in the host material 461. The singlet excitation energy level of the host material 461 is higher than the singlet excitation energy level of the guest material 462 (fluorescent material), and the triplet excitation energy level of the host material 461 is higher than that of the guest material 462 (fluorescent material). It is preferably lower than the triplet excitation energy level.

  As the host material 461, an anthracene derivative or a tetracene derivative is preferable. This is because these derivatives have high singlet excitation energy levels and low triplet excitation energy levels. Specifically, 9-phenyl-3- [4- (10-phenyl-9-anthryl) phenyl] -9H-carbazole (abbreviation: PCzPA), 3- [4- (1-naphthyl) -phenyl] -9 -Phenyl-9H-carbazole (abbreviation: PCPN), 9- [4- (10-phenyl-9-anthracenyl) phenyl] -9H-carbazole (abbreviation: CzPA), 7- [4- (10-phenyl-9- Anthryl) phenyl] -7H-dibenzo [c, g] carbazole (abbreviation: cgDBCzPA), 6- [3- (9,10-diphenyl-2-anthryl) phenyl] -benzo [b] naphtho [1,2-d ] Furan (abbreviation: 2 mBnfPPA), 9-phenyl-10- {4- (9-phenyl-9H-fluoren-9-yl) -biphenyl-4'-yl} anthrace (Abbreviation: FLPPA) and the like. Alternatively, 5,12-diphenyltetracene, 5,12-bis (biphenyl-2-yl) tetracene, and the like can be given.

  As the guest material 462 (fluorescent material), a pyrene derivative, anthracene derivative, triphenylene derivative, fluorene derivative, carbazole derivative, dibenzothiophene derivative, dibenzofuran derivative, dibenzoquinoxaline derivative, quinoxaline derivative, pyridine derivative, pyrimidine derivative, phenanthrene derivative, naphthalene derivative Etc. In particular, a pyrene derivative is preferable because of its high emission quantum yield. Specific examples of the pyrene derivative include N, N′-bis (3-methylphenyl) -N, N′-bis [3- (9-phenyl-9H-fluoren-9-yl) phenyl] pyrene-1,6. -Diamine (abbreviation: 1,6 mM emFLPAPrn), N, N'-diphenyl-N, N'-bis [4- (9-phenyl-9H-fluoren-9-yl) phenyl] pyrene-1,6-diamine (abbreviation) : 1,6FLPAPrn), N, N′-bis (dibenzofuran-2-yl) -N, N′-diphenylpyrene-1,6-diamine (abbreviation: 1,6FrAPrn), N, N′-bis (dibenzothiophene) -2-yl) -N, N′-diphenylpyrene-1,6-diamine (abbreviation: 1,6ThAPrn) and the like. Alternatively, the materials exemplified as the guest material 132 described in Embodiment 1 may be used.

<Materials that can be used for the light-emitting layer 470>
As a material that can be used for the light-emitting layer 470, a material that can be used for the light-emitting layer 130 described in Embodiment 1 may be used.

  Further, there is no limitation on the light emission colors of the light emitting material included in the light emitting layer 460 and the light emitting material included in the light emitting layer 470, and they may be the same or different. Since the light emission obtained from each is mixed and taken out of the device, the light emitting device can give white light when, for example, the light emission colors of both are complementary colors. In consideration of the reliability of the light-emitting element, the emission peak wavelength of the light-emitting material included in the light-emitting layer 460 is preferably shorter than that of the light-emitting material included in the light-emitting layer 470.

  Note that the light-emitting layer 460 and the light-emitting layer 470 can be formed by a method such as a vapor deposition method (including a vacuum vapor deposition method), an inkjet method, a coating method, or gravure printing.

  Note that the above structure can be combined with any of the other embodiments and the other structures in this embodiment as appropriate.

(Embodiment 4)
In this embodiment, a display device including the light-emitting element of one embodiment of the present invention will be described with reference to FIGS.

  6A is a block diagram illustrating a display device of one embodiment of the present invention, and FIG. 6B illustrates a pixel circuit included in the display device of one embodiment of the present invention. It is a circuit diagram.

<Description of display device>
A display device illustrated in FIG. 6A includes a region having a pixel of a display element (hereinafter referred to as a pixel portion 802) and a circuit portion (hereinafter, referred to as a pixel portion 802) having a circuit for driving the pixel. , A driver circuit portion 804), a circuit having an element protection function (hereinafter referred to as a protection circuit 806), and a terminal portion 807. Note that the protection circuit 806 may not be provided.

  Part or all of the driver circuit portion 804 is preferably formed over the same substrate as the pixel portion 802. Thereby, the number of parts and the number of terminals can be reduced. In the case where part or all of the driver circuit portion 804 is not formed over the same substrate as the pixel portion 802, part or all of the driver circuit portion 804 may be COG (Chip On Glass) or TAB (Tape). (Automated Bonding).

  The pixel portion 802 includes a circuit (hereinafter referred to as a pixel circuit 801) for driving a plurality of display elements arranged in X rows (X is a natural number of 2 or more) and Y columns (Y is a natural number of 2 or more). The driver circuit portion 804 supplies a signal for selecting a pixel (scanning signal) (hereinafter referred to as a scanning line driving circuit 804a) and a signal (data signal) for driving a display element of the pixel. A driver circuit such as a circuit (hereinafter, a signal line driver circuit 804b) is included.

  The scan line driver circuit 804a includes a shift register and the like. The scan line driver circuit 804a receives a signal for driving the shift register via the terminal portion 807 and outputs a signal. For example, the scan line driver circuit 804a receives a start pulse signal, a clock signal, and the like and outputs a pulse signal. The scan line driver circuit 804a has a function of controlling the potential of a wiring to which a scan signal is supplied (hereinafter referred to as scan lines GL_1 to GL_X). Note that a plurality of scan line driver circuits 804a may be provided, and the scan lines GL_1 to GL_X may be divided and controlled by the plurality of scan line driver circuits 804a. Alternatively, the scan line driver circuit 804a has a function of supplying an initialization signal. Note that the present invention is not limited to this, and the scan line driver circuit 804a can supply another signal.

  The signal line driver circuit 804b includes a shift register and the like. In addition to a signal for driving the shift register, the signal line driver circuit 804b receives a signal (image signal) that is a source of a data signal through the terminal portion 807. The signal line driver circuit 804b has a function of generating a data signal to be written in the pixel circuit 801 based on the image signal. In addition, the signal line driver circuit 804b has a function of controlling output of a data signal in accordance with a pulse signal obtained by inputting a start pulse, a clock signal, or the like. The signal line driver circuit 804b has a function of controlling the potential of a wiring to which a data signal is supplied (hereinafter referred to as data lines DL_1 to DL_Y). Alternatively, the signal line driver circuit 804b has a function of supplying an initialization signal. Note that the present invention is not limited to this, and the signal line driver circuit 804b can supply another signal.

  The signal line driver circuit 804b is configured using a plurality of analog switches, for example. The signal line driver circuit 804b can output a signal obtained by time-dividing an image signal as a data signal by sequentially turning on a plurality of analog switches. Alternatively, the signal line driver circuit 804b may be formed using a shift register or the like.

  Each of the plurality of pixel circuits 801 receives a pulse signal through one of the plurality of scanning lines GL to which the scanning signal is applied, and receives the data signal through one of the plurality of data lines DL to which the data signal is applied. Entered. In each of the plurality of pixel circuits 801, writing and holding of data signals is controlled by the scanning line driver circuit 804a. For example, the pixel circuit 801 in the m-th row and the n-th column receives a pulse signal from the scan line driver circuit 804a through the scan line GL_m (m is a natural number equal to or less than X), and the data line DL_n according to the potential of the scan line GL_m. A data signal is input from the signal line driver circuit 804b through (n is a natural number equal to or less than Y).

  The protection circuit 806 illustrated in FIG. 6A is connected to the scan line GL which is a wiring between the scan line driver circuit 804a and the pixel circuit 801, for example. Alternatively, the protection circuit 806 is connected to the data line DL that is a wiring between the signal line driver circuit 804 b and the pixel circuit 801. Alternatively, the protection circuit 806 can be connected to a wiring between the scan line driver circuit 804 a and the terminal portion 807. Alternatively, the protection circuit 806 can be connected to a wiring between the signal line driver circuit 804 b and the terminal portion 807. Note that the terminal portion 807 is a portion where a terminal for inputting a power supply, a control signal, and an image signal from an external circuit to the display device is provided.

  The protection circuit 806 is a circuit that brings a wiring into a conductive state when a potential outside a certain range is applied to the wiring to which the protection circuit 806 is connected.

  As shown in FIG. 6A, by providing a protection circuit 806 in each of the pixel portion 802 and the driver circuit portion 804, resistance of the display device to an overcurrent generated by ESD (Electro Static Discharge) or the like is increased. be able to. However, the structure of the protection circuit 806 is not limited thereto, and for example, a structure in which the protection circuit 806 is connected to the scan line driver circuit 804a or a structure in which the protection circuit 806 is connected to the signal line driver circuit 804b can be employed. Alternatively, the protective circuit 806 can be connected to the terminal portion 807.

  6A illustrates an example in which the driver circuit portion 804 is formed using the scan line driver circuit 804a and the signal line driver circuit 804b; however, the present invention is not limited to this structure. For example, a structure in which only the scan line driver circuit 804a is formed and a substrate on which a separately prepared signal line driver circuit is formed (for example, a driver circuit substrate formed of a single crystal semiconductor film or a polycrystalline semiconductor film) is mounted. Also good.

<Configuration example of pixel circuit>
A plurality of pixel circuits 801 illustrated in FIG. 6A can have a structure illustrated in FIG. 6B, for example.

  A pixel circuit 801 illustrated in FIG. 6B includes transistors 852 and 854, a capacitor 862, and a light-emitting element 872.

  One of a source electrode and a drain electrode of the transistor 852 is electrically connected to a wiring to which a data signal is supplied (hereinafter referred to as a signal line DL_n). Further, the gate electrode of the transistor 852 is electrically connected to a wiring to which a gate signal is supplied (hereinafter referred to as a scanning line GL_m).

  The transistor 852 has a function of controlling data writing of the data signal.

  One of the pair of electrodes of the capacitor 862 is electrically connected to a wiring to which a potential is applied (hereinafter referred to as a potential supply line VL_a), and the other is electrically connected to the other of the source electrode and the drain electrode of the transistor 852. Is done.

  The capacitor 862 functions as a storage capacitor for storing written data.

  One of a source electrode and a drain electrode of the transistor 854 is electrically connected to the potential supply line VL_a. Further, the gate electrode of the transistor 854 is electrically connected to the other of the source electrode and the drain electrode of the transistor 852.

  One of an anode and a cathode of the light-emitting element 872 is electrically connected to the potential supply line VL_b, and the other is electrically connected to the other of the source electrode and the drain electrode of the transistor 854.

  As the light-emitting element 872, the light-emitting element described in any of Embodiments 1 to 3 can be used.

  Note that one of the potential supply line VL_a and the potential supply line VL_b is supplied with the high power supply potential VDD, and the other is supplied with the low power supply potential VSS.

  In the display device including the pixel circuit 801 in FIG. 6B, for example, the pixel circuit 801 in each row is sequentially selected by the scan line driver circuit 804a illustrated in FIG. Write data.

  The pixel circuit 801 in which data is written is brought into a holding state when the transistor 852 is turned off. Further, the amount of current flowing between the source electrode and the drain electrode of the transistor 854 is controlled in accordance with the potential of the written data signal, and the light-emitting element 872 emits light with luminance corresponding to the flowing current amount. By sequentially performing this for each row, an image can be displayed.

  The light-emitting element of one embodiment of the present invention can be applied to an active matrix method in which an active element is included in a pixel of a display device or a passive matrix method in which an active element is not included in a pixel of a display device. .

  In the active matrix system, not only transistors but also various active elements (active elements and nonlinear elements) can be used as active elements (active elements and nonlinear elements). For example, MIM (Metal Insulator Metal) or TFD (Thin Film Diode) can be used. Since these elements have few manufacturing steps, manufacturing cost can be reduced or yield can be improved. Alternatively, since these elements have small element sizes, the aperture ratio can be improved, and power consumption and luminance can be increased.

  As a method other than the active matrix method, a passive matrix type that does not use an active element (an active element or a non-linear element) can be used. Since no active element (active element or non-linear element) is used, the number of manufacturing steps is small, so that manufacturing costs can be reduced or yield can be improved. Alternatively, since an active element (an active element or a non-linear element) is not used, an aperture ratio can be improved, power consumption can be reduced, or luminance can be increased.

  The structure described in this embodiment can be combined as appropriate with any of the structures described in the other embodiments.

(Embodiment 5)
In this embodiment, a display device including the light-emitting element of one embodiment of the present invention and an electronic device in which the input device is attached to the display device will be described with reference to FIGS.

<Description 1 regarding touch panel>
Note that in this embodiment, a touch panel 2000 including a display device and an input device is described as an example of an electronic device. A case where a touch sensor is used as an example of the input device will be described.

  7A and 7B are perspective views of the touch panel 2000. FIG. 7A and 7B, typical components of the touch panel 2000 are shown for clarity.

  The touch panel 2000 includes a display device 2501 and a touch sensor 2595 (see FIG. 7B). The touch panel 2000 includes a substrate 2510, a substrate 2570, and a substrate 2590. Note that the substrate 2510, the substrate 2570, and the substrate 2590 are all flexible. Note that any one or all of the substrate 2510, the substrate 2570, and the substrate 2590 may not have flexibility.

  The display device 2501 includes a plurality of pixels over the substrate 2510 and a plurality of wirings 2511 that can supply signals to the pixels. The plurality of wirings 2511 are routed to the outer periphery of the substrate 2510, and a part of them constitutes a terminal 2519. A terminal 2519 is electrically connected to the FPC 2509 (1).

  The substrate 2590 includes a touch sensor 2595 and a plurality of wirings 2598 electrically connected to the touch sensor 2595. The plurality of wirings 2598 are drawn around the outer periphery of the substrate 2590, and a part of them constitutes a terminal. The terminal is electrically connected to the FPC 2509 (2). Note that in FIG. 7B, electrodes, wirings, and the like of the touch sensor 2595 provided on the back side of the substrate 2590 (the side facing the substrate 2510) are shown by solid lines for clarity.

  As the touch sensor 2595, for example, a capacitive touch sensor can be used. Examples of the electrostatic capacity method include a surface electrostatic capacity method and a projection electrostatic capacity method.

  As the projected capacitance method, there are mainly a self-capacitance method and a mutual capacitance method due to a difference in driving method. The mutual capacitance method is preferable because simultaneous multipoint detection is possible.

  Note that a touch sensor 2595 illustrated in FIG. 7B has a structure to which a projected capacitive touch sensor is applied.

  Note that as the touch sensor 2595, various sensors that can detect the proximity or contact of a detection target such as a finger can be used.

  The projected capacitive touch sensor 2595 includes an electrode 2591 and an electrode 2592. The electrode 2591 is electrically connected to any of the plurality of wirings 2598, and the electrode 2592 is electrically connected to any other of the plurality of wirings 2598.

  As shown in FIGS. 7A and 7B, the electrode 2592 has a shape in which a plurality of quadrilaterals repeatedly arranged in one direction are connected at corners.

  The electrode 2591 has a quadrangular shape and is repeatedly arranged in a direction intersecting with the direction in which the electrode 2592 extends.

  The wiring 2594 is electrically connected to two electrodes 2591 that sandwich the electrode 2592. At this time, a shape in which the area of the intersection of the electrode 2592 and the wiring 2594 is as small as possible is preferable. Thereby, the area of the area | region in which the electrode is not provided can be reduced, and the dispersion | variation in the transmittance | permeability can be reduced. As a result, variation in luminance of light transmitted through the touch sensor 2595 can be reduced.

  Note that the shapes of the electrode 2591 and the electrode 2592 are not limited thereto, and various shapes can be employed. For example, a plurality of electrodes 2591 may be arranged so as not to have a gap as much as possible, and a plurality of electrodes 2592 may be provided apart from each other so as to form a region that does not overlap with the electrodes 2591 with an insulating layer interposed therebetween. At this time, it is preferable to provide a dummy electrode electrically insulated from two adjacent electrodes 2592 because the area of regions having different transmittances can be reduced.

<Description of display device>
Next, details of the display device 2501 will be described with reference to FIG. FIG. 8A corresponds to a cross-sectional view taken along dashed-dotted line X1-X2 in FIG.

  The display device 2501 includes a plurality of pixels arranged in a matrix. The pixel includes a display element and a pixel circuit that drives the display element.

  In the following description, a case where a light-emitting element that emits white light is applied to a display element will be described; however, the display element is not limited to this. For example, light emitting elements having different emission colors may be applied so that the color of light emitted from each adjacent pixel is different.

For example, the substrate 2510 and the substrate 2570 have a water vapor transmission rate of 1 × 10 ⁻⁵ g · m ⁻² · day ⁻¹ or less, preferably 1 × 10 ⁻⁶ g · m ⁻² · day ⁻¹ or less. A flexible material can be preferably used. Alternatively, it is preferable to use a material in which the thermal expansion coefficient of the substrate 2510 and the thermal expansion coefficient of the substrate 2570 are approximately equal. For example, a material having a linear expansion coefficient of 1 × 10 ⁻³ / K or less, preferably 5 × 10 ⁻⁵ / K or less, more preferably 1 × 10 ⁻⁵ / K or less can be suitably used.

  Note that the substrate 2510 is a stack including an insulating layer 2510a that prevents diffusion of impurities into the light-emitting element, a flexible substrate 2510b, and an adhesive layer 2510c that bonds the insulating layer 2510a and the flexible substrate 2510b. . The substrate 2570 is a stack including an insulating layer 2570a that prevents diffusion of impurities into the light-emitting element, a flexible substrate 2570b, and an adhesive layer 2570c that bonds the insulating layer 2570a and the flexible substrate 2570b. .

  As the adhesive layer 2510c and the adhesive layer 2570c, for example, polyester, polyolefin, polyamide (nylon, aramid, or the like), polyimide, polycarbonate, acrylic resin, polyurethane, or epoxy resin can be used. Alternatively, a material including a resin having a siloxane bond such as silicone can be used.

  In addition, a sealing layer 2560 is provided between the substrate 2510 and the substrate 2570. The sealing layer 2560 preferably has a refractive index larger than that of air. In addition, as illustrated in FIG. 8A, in the case where light is extracted to the sealing layer 2560 side, the sealing layer 2560 can also serve as an optical bonding layer.

  Further, a sealing material may be formed on the outer peripheral portion of the sealing layer 2560. By using the sealant, the light-emitting element 2550R can be provided in the region surrounded by the substrate 2510, the substrate 2570, the sealing layer 2560, and the sealant. Note that the sealing layer 2560 may be filled with an inert gas (such as nitrogen or argon). In addition, a drying material may be provided in the inert gas to adsorb moisture or the like. Further, it may be filled with an ultraviolet curable resin or a thermosetting resin. For example, PVC (polyvinyl chloride) resin, acrylic resin, polyimide resin, epoxy resin, silicone resin, PVB (polyvinyl butyral) resin. Alternatively, EVA (ethylene vinyl acetate) resin can be used. Moreover, as the above-mentioned sealing material, for example, it is preferable to use an epoxy resin or glass frit. As a material used for the sealant, a material that does not transmit moisture and oxygen is preferably used.

  In addition, the display device 2501 includes a pixel 2502R. In addition, the pixel 2502R includes a light emitting module 2580R.

  The pixel 2502R includes a light-emitting element 2550R and a transistor 2502t that can supply power to the light-emitting element 2550R. Note that the transistor 2502t functions as part of the pixel circuit. The light emitting module 2580R includes a light emitting element 2550R and a colored layer 2567R.

  The light-emitting element 2550R includes a lower electrode, an upper electrode, and an EL layer between the lower electrode and the upper electrode. As the light-emitting element 2550R, for example, the light-emitting element described in any of Embodiments 1 to 3 can be used.

  Further, a microcavity structure may be employed between the lower electrode and the upper electrode to increase the light intensity at a specific wavelength.

  In the case where the sealing layer 2560 is provided on the light extraction side, the sealing layer 2560 is in contact with the light-emitting element 2550R and the coloring layer 2567R.

  The coloring layer 2567R is in a position overlapping with the light-emitting element 2550R. Thus, part of the light emitted from the light emitting element 2550R passes through the colored layer 2567R and is emitted to the outside of the light emitting module 2580R in the direction of the arrow shown in the drawing.

  The display device 2501 is provided with a light-blocking layer 2567BM in the direction of emitting light. The light-blocking layer 2567BM is provided so as to surround the colored layer 2567R.

  The coloring layer 2567R may have a function of transmitting light in a specific wavelength band, for example, a color filter that transmits light in a red wavelength band, a color filter that transmits light in a green wavelength band, A color filter that transmits light in the blue wavelength band, a color filter that transmits light in the yellow wavelength band, and the like can be used. Each color filter can be formed using a variety of materials by a printing method, an inkjet method, an etching method using a photolithography technique, or the like.

  In addition, the display device 2501 is provided with an insulating layer 2521. The insulating layer 2521 covers the transistor 2502t. Note that the insulating layer 2521 has a function of planarizing unevenness caused by the pixel circuit. Further, the insulating layer 2521 may have a function of suppressing impurity diffusion. Accordingly, a decrease in reliability of the transistor 2502t and the like due to impurity diffusion can be suppressed.

  The light-emitting element 2550R is formed above the insulating layer 2521. In addition, the lower electrode included in the light-emitting element 2550R is provided with a partition wall 2528 which overlaps with an end portion of the lower electrode. Note that a spacer for controlling the distance between the substrate 2510 and the substrate 2570 may be formed over the partition wall 2528.

  The scan line driver circuit 2503g (1) includes a transistor 2503t and a capacitor 2503c. Note that the driver circuit can be formed over the same substrate in the same process as the pixel circuit.

  A wiring 2511 capable of supplying a signal is provided over the substrate 2510. A terminal 2519 is provided over the wiring 2511. In addition, the FPC 2509 (1) is electrically connected to the terminal 2519. The FPC 2509 (1) has a function of supplying a video signal, a clock signal, a start signal, a reset signal, and the like. Note that a printed wiring board (PWB: Printed Wiring Board) may be attached to the FPC 2509 (1).

  Further, transistors with various structures can be used for the display device 2501. FIG. 8A illustrates the case where a bottom-gate transistor is used; however, the invention is not limited to this. For example, a top-gate transistor illustrated in FIG. It is good also as a structure applied to.

  There are no particular limitations on the polarities of the transistors 2502t and 2503t, and a structure including N-type and P-type transistors or a structure including only one of an N-type transistor and a P-type transistor may be used. . Further, there is no particular limitation on the crystallinity of the semiconductor film used for the transistors 2502t and 2503t. For example, an amorphous semiconductor film or a crystalline semiconductor film can be used. As the semiconductor material, a Group 13 semiconductor (eg, a semiconductor containing gallium), a Group 14 semiconductor (eg, a semiconductor containing silicon), a compound semiconductor (including an oxide semiconductor), an organic semiconductor, or the like is used. it can. By using an oxide semiconductor with an energy gap of 2 eV or more, preferably 2.5 eV or more, more preferably 3 eV or more for either or both of the transistor 2502t and the transistor 2503t, the off-state current of the transistor can be reduced. Therefore, it is preferable. Examples of the oxide semiconductor include In—Ga oxide, In—M—Zn oxide (M is aluminum (Al), gallium (Ga), yttrium (Y), zirconium (Zr), lanthanum (La), cerium) (Ce), tin (Sn), hafnium (Hf), or neodymium (Nd)).

<Explanation about touch sensor>
Next, details of the touch sensor 2595 will be described with reference to FIG. FIG. 8C corresponds to a cross-sectional view taken along dashed-dotted line X3-X4 in FIG.

  The touch sensor 2595 includes electrodes 2591 and electrodes 2592 that are arranged in a staggered pattern on the substrate 2590, an insulating layer 2593 that covers the electrodes 2591 and 2592, and wiring 2594 that electrically connects adjacent electrodes 2591.

  The electrodes 2591 and 2592 are formed using a light-transmitting conductive material. As the light-transmitting conductive material, a conductive oxide such as indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zinc oxide to which gallium is added can be used. Note that a film containing graphene can also be used. The film containing graphene can be formed, for example, by reducing a film containing graphene oxide formed in a film shape. Examples of the reduction method include a method of applying heat.

  For example, after forming a light-transmitting conductive material over the substrate 2590 by a sputtering method, unnecessary portions are removed by various pattern formation techniques such as a photolithography method, so that the electrode 2591 and the electrode 2592 are formed. can do.

  As a material used for the insulating layer 2593, for example, an inorganic insulating material such as silicon oxide, silicon oxynitride, or aluminum oxide can be used in addition to a resin such as acrylic or epoxy, or a resin having a siloxane bond.

  An opening reaching the electrode 2591 is provided in the insulating layer 2593 so that the wiring 2594 is electrically connected to the adjacent electrode 2591. Since the light-transmitting conductive material can increase the aperture ratio of the touch panel, it can be preferably used for the wiring 2594. A material having higher conductivity than the electrodes 2591 and 2592 can be preferably used for the wiring 2594 because electric resistance can be reduced.

  The electrode 2592 extends in one direction, and a plurality of electrodes 2592 are provided in a stripe shape. The wiring 2594 is provided so as to intersect with the electrode 2592.

  A pair of electrodes 2591 is provided with one electrode 2592 interposed therebetween. The wiring 2594 electrically connects the pair of electrodes 2591.

  Note that the plurality of electrodes 2591 are not necessarily arranged in a direction orthogonal to the one electrode 2592, and may be arranged to form an angle of more than 0 degree and less than 90 degrees.

  The wiring 2598 is electrically connected to the electrode 2591 or the electrode 2592. In addition, part of the wiring 2598 functions as a terminal. As the wiring 2598, for example, a metal material such as aluminum, gold, platinum, silver, nickel, titanium, tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium, or an alloy material containing the metal material is used. it can.

  Note that an insulating layer that covers the insulating layer 2593 and the wiring 2594 may be provided to protect the touch sensor 2595.

  The connection layer 2599 electrically connects the wiring 2598 and the FPC 2509 (2).

  As the connection layer 2599, an anisotropic conductive film (ACF: Anisotropic Conductive Film), an anisotropic conductive paste (ACP: Anisotropic Conductive Paste), or the like can be used.

<Description 2 regarding touch panel>
Next, details of the touch panel 2000 will be described with reference to FIG. FIG. 9A corresponds to a cross-sectional view taken along dashed-dotted line X5-X6 in FIG.

  A touch panel 2000 illustrated in FIG. 9A has a structure in which the display device 2501 described in FIG. 8A and the touch sensor 2595 described in FIG.

  In addition to the structure described in FIGS. 8A and 8C, the touch panel 2000 illustrated in FIG. 9A includes an adhesive layer 2597 and an antireflection layer 2567p.

  The adhesive layer 2597 is provided in contact with the wiring 2594. Note that the adhesive layer 2597 attaches the substrate 2590 to the substrate 2570 so that the touch sensor 2595 overlaps the display device 2501. The adhesive layer 2597 preferably has a light-transmitting property. For the adhesive layer 2597, a thermosetting resin or an ultraviolet curable resin can be used. For example, an acrylic resin, a urethane resin, an epoxy resin, or a siloxane resin can be used.

  The antireflection layer 2567p is provided at a position overlapping the pixel. As the antireflection layer 2567p, for example, a circularly polarizing plate can be used.

  Next, a touch panel having a structure different from that illustrated in FIG. 9A will be described with reference to FIG.

  FIG. 9B is a cross-sectional view of the touch panel 2001. A touch panel 2001 illustrated in FIG. 9B is different from the touch panel 2000 illustrated in FIG. 9A in the position of the touch sensor 2595 with respect to the display device 2501. Here, different configurations will be described in detail, and the description of the touch panel 2000 is used for a portion where a similar configuration can be used.

  The coloring layer 2567R is in a position overlapping with the light-emitting element 2550R. In addition, the light-emitting element 2550R illustrated in FIG. 9B emits light to the side where the transistor 2502t is provided. Thus, part of the light emitted from the light emitting element 2550R passes through the colored layer 2567R and is emitted to the outside of the light emitting module 2580R in the direction of the arrow shown in the drawing.

  The touch sensor 2595 is provided on the substrate 2510 side of the display device 2501.

  An adhesive layer 2597 is provided between the substrate 2510 and the substrate 2590, and the display device 2501 and the touch sensor 2595 are attached to each other.

  As shown in FIGS. 9A and 9B, light emitted from the light emitting element may be emitted to one or both of the upper surface and the lower surface of the substrate.

<Explanation regarding touch panel drive method>
Next, an example of a touch panel driving method will be described with reference to FIG.

  FIG. 10A is a block diagram illustrating a structure of a mutual capacitive touch sensor. FIG. 10A shows a pulse voltage output circuit 2601 and a current detection circuit 2602. Note that in FIG. 10A, the electrode 2621 to which a pulse voltage is applied is illustrated as X1-X6, and the electrode 2622 for detecting a change in current is illustrated as Y1-Y6. FIG. 10A illustrates a capacitor 2603 formed by the overlap of the electrode 2621 and the electrode 2622. Note that the functions of the electrode 2621 and the electrode 2622 may be interchanged.

  The pulse voltage output circuit 2601 is a circuit for sequentially applying pulses to the wiring lines X1 to X6. When a pulse voltage is applied to the wiring of X1-X6, an electric field is generated between the electrode 2621 and the electrode 2622 forming the capacitor 2603. By utilizing the fact that the electric field generated between the electrodes causes a change in the mutual capacitance of the capacitor 2603 due to shielding or the like, it is possible to detect the proximity or contact of the detection object.

  The current detection circuit 2602 is a circuit for detecting a change in current in the wiring of Y1-Y6 due to a change in mutual capacitance in the capacitor 2603. In the wiring of Y1-Y6, there is no change in the current value detected when there is no proximity or contact with the detected object, but the current value when the mutual capacitance decreases due to the proximity or contact with the detected object. Detect changes that decrease. Note that current detection may be performed using an integration circuit or the like.

  Next, FIG. 10B shows a timing chart of input / output waveforms in the mutual capacitance type touch sensor shown in FIG. In FIG. 10B, the detection target is detected in each matrix in one frame period. FIG. 10B shows two cases, that is, a case where the detected object is not detected (non-touch) and a case where the detected object is detected (touch). In addition, about the wiring of Y1-Y6, the waveform made into the voltage value corresponding to the detected electric current value is shown.

  A pulse voltage is sequentially applied to the X1-X6 wiring, and the waveform of the Y1-Y6 wiring changes according to the pulse voltage. When there is no proximity or contact of the detection object, the waveform of Y1-Y6 changes uniformly according to the change of the voltage of the wiring of X1-X6. On the other hand, since the current value decreases at the location where the detection object is close or in contact, the waveform of the voltage value corresponding to this also changes.

  In this way, by detecting the change in mutual capacitance, the proximity or contact of the detection target can be detected.

<Explanation about sensor circuit>
10A illustrates a structure of a passive matrix touch sensor in which only a capacitor 2603 is provided at a wiring intersection as a touch sensor, an active matrix touch sensor including a transistor and a capacitor may be used. An example of a sensor circuit included in the active matrix touch sensor is shown in FIG.

  The sensor circuit illustrated in FIG. 11 includes a capacitor 2603, a transistor 2611, a transistor 2612, and a transistor 2613.

  The gate of the transistor 2613 is supplied with the signal G2, the voltage VRES is supplied to one of a source and a drain, and the other is electrically connected to one electrode of the capacitor 2603 and the gate of the transistor 2611. In the transistor 2611, one of a source and a drain is electrically connected to one of a source and a drain of the transistor 2612, and the voltage VSS is supplied to the other. In the transistor 2612, the gate is supplied with the signal G1, and the other of the source and the drain is electrically connected to the wiring ML. The voltage VSS is applied to the other electrode of the capacitor 2603.

  Next, the operation of the sensor circuit shown in FIG. 11 will be described. First, a potential for turning on the transistor 2613 is supplied as the signal G2, so that a potential corresponding to the voltage VRES is applied to the node n to which the gate of the transistor 2611 is connected. Next, a potential for turning off the transistor 2613 is supplied as the signal G2, so that the potential of the node n is held.

  Subsequently, the potential of the node n changes from VRES as the mutual capacitance of the capacitor 2603 changes due to the proximity or contact of a detection object such as a finger.

  In the reading operation, a potential for turning on the transistor 2612 is supplied to the signal G1. The current flowing through the transistor 2611, that is, the current flowing through the wiring ML is changed in accordance with the potential of the node n. By detecting this current, the proximity or contact of the detection object can be detected.

  As the transistor 2611, the transistor 2612, and the transistor 2613, an oxide semiconductor layer is preferably used for a semiconductor layer in which a channel region is formed. In particular, when such a transistor is used as the transistor 2613, the potential of the node n can be held for a long time, and the frequency of the operation of supplying VRES to the node n (refresh operation) can be reduced. it can.

  The structure described in this embodiment can be combined as appropriate with any of the structures described in the other embodiments.

(Embodiment 6)
In this embodiment, a display module and an electronic device each including the light-emitting element of one embodiment of the present invention will be described with reference to FIGS.

<Explanation about display module>
A display module 8000 illustrated in FIG. 12 includes a touch sensor 8004 connected to the FPC 8003, a display device 8006 connected to the FPC 8005, a frame 8009, a printed circuit board 8010, and a battery 8011 between an upper cover 8001 and a lower cover 8002. .

  The light-emitting element of one embodiment of the present invention can be used for the display device 8006, for example.

  The shapes and dimensions of the upper cover 8001 and the lower cover 8002 can be changed as appropriate in accordance with the sizes of the touch sensor 8004 and the display device 8006.

  As the touch sensor 8004, a resistive touch sensor or a capacitive touch sensor can be used by being superimposed on the display device 8006. In addition, the counter substrate (sealing substrate) of the display device 8006 can have a touch sensor function. In addition, an optical sensor may be provided in each pixel of the display device 8006 to provide an optical touch sensor.

  The frame 8009 has a function as an electromagnetic shield for blocking electromagnetic waves generated by the operation of the printed board 8010 in addition to a protective function of the display device 8006. The frame 8009 may have a function as a heat sink.

  The printed board 8010 includes a power supply circuit, a signal processing circuit for outputting a video signal and a clock signal. As a power supply for supplying power to the power supply circuit, an external commercial power supply may be used, or a power supply using a battery 8011 provided separately may be used. The battery 8011 can be omitted when a commercial power source is used.

  The display module 8000 may be additionally provided with a member such as a polarizing plate, a retardation plate, or a prism sheet.

<Explanation about electronic equipment>
13A to 13G illustrate electronic devices. These electronic devices include a housing 9000, a display portion 9001, a speaker 9003, operation keys 9005 (including a power switch or operation switch), a connection terminal 9006, and a sensor 9007 (force, displacement, position, speed, acceleration, angular velocity, Includes functions to measure rotation speed, distance, light, liquid, magnetism, temperature, chemical, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor or infrared ), A microphone 9008, and the like.

  The electronic devices illustrated in FIGS. 13A to 13G can have a variety of functions. For example, a function for displaying various information (still images, moving images, text images, etc.) on the display unit, a touch sensor function, a function for displaying a calendar, date or time, etc., a function for controlling processing by various software (programs) , Wireless communication function, function to connect to various computer networks using wireless communication function, function to transmit or receive various data using wireless communication function, read program or data recorded in recording medium A function of displaying on the display portion can be provided. Note that the functions of the electronic devices illustrated in FIGS. 13A to 13G are not limited to these, and can have various functions. Although not illustrated in FIGS. 13A to 13G, the electronic device may have a plurality of display portions. In addition, the electronic device is equipped with a camera, etc., to capture still images, to capture moving images, to store captured images on a recording medium (externally or built into the camera), and to display captured images on the display unit And the like.

  Details of the electronic devices illustrated in FIGS. 13A to 13G are described below.

  FIG. 13A is a perspective view showing a portable information terminal 9100. A display portion 9001 included in the portable information terminal 9100 has flexibility. Therefore, the display portion 9001 can be incorporated along the curved surface of the curved housing 9000. Further, the display portion 9001 includes a touch sensor and can be operated by touching the screen with a finger, a stylus, or the like. For example, an application can be activated by touching an icon displayed on the display unit 9001.

  FIG. 13B is a perspective view showing the portable information terminal 9101. The portable information terminal 9101 has one or a plurality of functions selected from, for example, a telephone, a notebook, an information browsing device, or the like. Specifically, it can be used as a smartphone. Note that the portable information terminal 9101 is illustrated with the speaker 9003, the connection terminal 9006, the sensor 9007, and the like omitted, but can be provided at the same position as the portable information terminal 9100 illustrated in FIG. Further, the portable information terminal 9101 can display characters and image information on the plurality of surfaces. For example, three operation buttons 9050 (also referred to as operation icons or simply icons) can be displayed on one surface of the display portion 9001. Further, information 9051 indicated by a broken-line rectangle can be displayed on another surface of the display portion 9001. As an example of the information 9051, a display for notifying an incoming call such as an e-mail, SNS (social networking service), a telephone call, a title such as an e-mail or SNS, a sender name such as an e-mail or SNS, a date and time, and a time , Battery level, antenna reception strength and so on. Alternatively, an operation button 9050 or the like may be displayed instead of the information 9051 at a position where the information 9051 is displayed.

  FIG. 13C is a perspective view showing the portable information terminal 9102. The portable information terminal 9102 has a function of displaying information on three or more surfaces of the display portion 9001. Here, an example is shown in which information 9052, information 9053, and information 9054 are displayed on different planes. For example, the user of the portable information terminal 9102 can check the display (information 9053 here) in a state where the portable information terminal 9102 is stored in the chest pocket of clothes. Specifically, the telephone number or name of the caller of the incoming call is displayed at a position where it can be observed from above portable information terminal 9102. The user can check the display and determine whether to receive a call without taking out the portable information terminal 9102 from the pocket.

  FIG. 13D is a perspective view showing a wristwatch-type portable information terminal 9200. The portable information terminal 9200 can execute various applications such as a mobile phone, electronic mail, text browsing and creation, music playback, Internet communication, and computer games. Further, the display portion 9001 is provided with a curved display surface, and can perform display along the curved display surface. In addition, the portable information terminal 9200 can execute short-range wireless communication with a communication standard. For example, it is possible to talk hands-free by communicating with a headset capable of wireless communication. In addition, the portable information terminal 9200 includes a connection terminal 9006 and can directly exchange data with other information terminals via a connector. Charging can also be performed through the connection terminal 9006. Note that the charging operation may be performed by wireless power feeding without using the connection terminal 9006.

  13E, 13F, and 13G are perspective views illustrating a foldable portable information terminal 9201. FIG. 13E is a perspective view of a state in which the portable information terminal 9201 is expanded, and FIG. 13F is a state in the middle of changing from one of the expanded state or the folded state of the portable information terminal 9201 to the other. FIG. 13G is a perspective view of the portable information terminal 9201 folded. The portable information terminal 9201 is excellent in portability in the folded state, and in the expanded state, the portable information terminal 9201 is excellent in display listability due to a seamless wide display area. A display portion 9001 included in the portable information terminal 9201 is supported by three housings 9000 connected by a hinge 9055. By bending between the two housings 9000 via the hinge 9055, the portable information terminal 9201 can be reversibly deformed from the expanded state to the folded state. For example, the portable information terminal 9201 can be bent with a curvature radius of 1 mm to 150 mm.

  The electronic device described in this embodiment includes a display portion for displaying some information. Note that the light-emitting element of one embodiment of the present invention can also be applied to an electronic device having no display portion. In addition, in the display portion of the electronic device described in this embodiment, an example of a configuration that has flexibility and can display along a curved display surface, or a configuration of a foldable display portion is given. However, the present invention is not limited to this, and may have a configuration in which display is performed on a flat portion without having flexibility.

  The structure described in this embodiment can be combined as appropriate with any of the structures described in the other embodiments.

(Embodiment 7)
In this embodiment, an example of a lighting device to which the light-emitting element which is one embodiment of the present invention is applied will be described with reference to FIGS.

  FIG. 14 illustrates an example in which the light-emitting element is used as an indoor lighting device 8501. Note that since the light-emitting element can have a large area, a large-area lighting device can be formed. In addition, by using a housing having a curved surface, the lighting device 8502 in which the light-emitting region has a curved surface can be formed. The light-emitting element described in this embodiment is thin and has a high degree of freedom in housing design. Therefore, it is possible to form a lighting device with various designs. Further, a large lighting device 8503 may be provided on the indoor wall surface. Alternatively, the lighting devices 8501, 8502, and 8503 may be provided with touch sensors to turn the power on or off.

  In addition, by using the light-emitting element on the surface side of the table, the lighting device 8504 having a function as a table can be obtained. Note that a lighting device having a function as furniture can be obtained by using a light-emitting element as part of other furniture.

  As described above, various lighting devices to which the light-emitting element is applied can be obtained. Note that these lighting devices are included in one embodiment of the present invention.

  The structure described in this embodiment can be combined as appropriate with any of the structures described in the other embodiments.

100 EL layer 101 Electrode 102 Electrode 111 Hole injection layer 112 Hole transport layer 117 Electron transport layer 118 Electron injection layer 130 Light emitting layer 131 Host material 131_1 Organic compound 131_2 Organic compound 132 Guest material 150 Light emitting element 401 Electrode 402 Electrode 411 Hole Injection layer 412 Hole transport layer 413 Electron transport layer 414 Electron injection layer 415 Hole injection layer 416 Hole transport layer 417 Electron transport layer 418 Electron injection layer 420 Light emitting layer 421 Host material 421_1 Organic compound 421_2 Organic compound 422 Guest material 430 Light emission Layer 431 Host material 431_1 Organic compound 431_2 Organic compound 432 Guest material 441 Light emitting unit 442 Light emitting unit 445 Charge generation layer 446 Light emitting unit 447 Light emitting unit 450 Light emitting element 452 Light emitting element 460 Light emitting layer 61 Host material 462 Guest material 470 Light emitting layer 471 Host material 471_1 Organic compound 471_2 Organic compound 472 Guest material 801 Pixel circuit 802 Pixel portion 804 Driver circuit portion 804a Scan line driver circuit 804b Signal line driver circuit 806 Protection circuit 807 Terminal portion 852 Transistor 854 Transistor 862 Capacitor element 872 Light emitting element 2000 Touch panel 2001 Touch panel 2501 Display device 2502R Pixel 2502t Transistor 2503c Capacitor element 2503g Scan line driver circuit 2503t Transistor 2509 FPC
2510 Substrate 2510a Insulating layer 2510b Flexible substrate 2510c Adhesive layer 2511 Wiring 2519 Terminal 2521 Insulating layer 2528 Partition 2550R Light emitting element 2560 Sealing layer 2567BM Light shielding layer 2567p Antireflection layer 2567R Colored layer 2570 Substrate 2570a Insulating layer 2570b Flexible substrate 2570c Adhesive layer 2580R Light emitting module 2590 Substrate 2591 Electrode 2592 Electrode 2593 Insulating layer 2594 Wiring 2595 Touch sensor 2597 Adhesive layer 2598 Wiring 2599 Connection layer 2601 Pulse voltage output circuit 2602 Current detection circuit 2603 Capacitance 2611 Transistor 2612 Transistor 2613 Transistor 2621 Electrode 2622 Electrode 8000 Display Module 8001 Upper cover 8002 Lower cover 8003 FPC
8004 Touch sensor 8005 FPC
8006 Display device 8009 Frame 8010 Printed circuit board 8011 Battery 8501 Illumination device 8502 Illumination device 8503 Illumination device 8504 Illumination device 9000 Case 9001 Display unit 9003 Speaker 9005 Operation key 9006 Connection terminal 9007 Sensor 9008 Microphone 9050 Operation button 9051 Information 9052 Information 9053 Information 9054 Information 9055 hinge 9100 portable information terminal 9101 portable information terminal 9102 portable information terminal 9200 portable information terminal 9201 portable information terminal

Claims (27)

A pair of electrodes;
An EL layer provided between the pair of electrodes;
A light emitting device comprising:
The EL layer has a host material and a guest material,
The host material has a function capable of exhibiting thermally activated delayed fluorescence at room temperature,
The guest material has a function of exhibiting fluorescence,
The guest material has a second excited triplet energy level equal to or higher than a lowest excited singlet energy level of the guest material.
A light emitting element characterized by the above. A pair of electrodes;
An EL layer provided between the pair of electrodes;
A light emitting device comprising:
The EL layer has a host material and a guest material,
The host material has a function capable of exhibiting thermally activated delayed fluorescence at room temperature,
The guest material has a function of exhibiting fluorescence,
A second excited triplet energy level of the guest material is equal to or higher than a lowest excited triplet energy level of the host material;
The lowest excited triplet energy level of the host material is greater than or equal to the lowest excited triplet energy level of the guest material;
A light emitting element characterized by the above. In claim 2,
The second excited triplet energy level of the guest material is greater than or equal to the lowest excited singlet energy level of the host material;
A light emitting element characterized by the above. In claim 2 or claim 3,
The difference between the lowest excited triplet energy level of the host material and the lowest excited triplet energy level of the guest material is 0.5 eV or more.
A light emitting element characterized by the above. In claim 2 or claim 3,
The emission energy of thermally activated delayed fluorescence of the host material is greater than or equal to the phosphorescence emission energy of the guest material.
A light emitting element characterized by the above. In claim 5,
The difference between the thermally activated delayed fluorescence emission energy of the host material and the phosphorescence emission energy of the guest material is 0.5 eV or more.
A light emitting element characterized by the above. A pair of electrodes;
An EL layer provided between the pair of electrodes;
A light emitting device comprising:
The EL layer has a host material and a guest material,
The host material has a function capable of exhibiting thermally activated delayed fluorescence at room temperature,
The guest material has a function of exhibiting fluorescence,
A second excited triplet energy level of the guest material is equal to or higher than a lowest excited triplet energy level of the host material;
The lowest excited triplet energy level of the host material is greater than or equal to the lowest excited singlet energy level of the guest material;
A light emitting element characterized by the above. In claim 7,
The second excited triplet energy level of the guest material is greater than or equal to the lowest excited singlet energy level of the host material;
A light emitting element characterized by the above. In claim 7 or claim 8,
The emission energy of thermally activated delayed fluorescence of the host material is greater than or equal to the fluorescence emission energy of the guest material,
A light emitting element characterized by the above. In claims 1 to 9,
The difference between the lowest excited singlet energy level of the host material and the lowest excited triplet energy level of the host material is more than 0 eV and not more than 0.2 eV.
A light emitting element characterized by the above. A pair of electrodes;
An EL layer provided between the pair of electrodes;
A light emitting device comprising:
The EL layer has a host material and a guest material,
The host material has a first organic compound and a second organic compound,
The exciplex formed by the first organic compound and the second organic compound has a function capable of exhibiting thermally activated delayed fluorescence at room temperature,
The guest material has a function of exhibiting fluorescence,
The guest material has a second excited triplet energy level equal to or higher than a lowest excited singlet energy level of the guest material.
A light emitting element characterized by the above. A pair of electrodes;
An EL layer provided between the pair of electrodes;
A light emitting device comprising:
The EL layer has a host material and a guest material,
The host material has a first organic compound and a second organic compound,
The exciplex formed by the first organic compound and the second organic compound has a function capable of exhibiting thermally activated delayed fluorescence at room temperature,
The guest material has a function of exhibiting fluorescence,
The guest material has a second excited triplet energy level equal to or higher than a lowest excited triplet energy level of the exciplex,
The lowest excited triplet energy level of the exciplex is greater than or equal to the lowest excited triplet energy level of the guest material;
A light emitting element characterized by the above. In claim 12,
The second excited triplet energy level of the guest material is greater than or equal to the lowest excited singlet energy level of the exciplex;
A light emitting element characterized by the above. In claim 12 or claim 13,
The difference between the lowest excited triplet energy level of the exciplex and the lowest excited triplet energy level of the guest material is 0.5 eV or more.
A light emitting element characterized by the above. In claim 12 or claim 13,
The emission energy of the thermally activated delayed phosphor of the exciplex is greater than or equal to the phosphorescence emission energy of the guest material,
A light emitting element characterized by the above. In claim 15,
The difference between the emission energy of the thermally activated delayed phosphor of the exciplex and the phosphorescence emission energy of the guest material is 0.5 eV or more,
A light emitting element characterized by the above. A pair of electrodes;
An EL layer provided between the pair of electrodes;
A light emitting device comprising:
The EL layer has a host material and a guest material,
The host material has a first organic compound and a second organic compound,
The exciplex formed by the first organic compound and the second organic compound has a function capable of exhibiting thermally activated delayed fluorescence at room temperature,
The guest material has a function of exhibiting fluorescence,
The guest material has a second excited triplet energy level equal to or higher than a lowest excited triplet energy level of the exciplex,
The lowest excited triplet energy level of the exciplex is greater than or equal to the lowest excited singlet energy level of the guest material;
A light emitting element characterized by the above. In claim 17,
The second excited triplet energy level of the guest material is greater than or equal to the lowest excited singlet energy level of the exciplex;
A light emitting element characterized by the above. In claim 17 or claim 18,
The emission energy of thermally activated delayed fluorescence of the exciplex is greater than or equal to the fluorescence emission energy of the guest material,
A light emitting element characterized by the above. In claims 11 to 19,
The difference between the lowest excited singlet energy level of the exciplex and the lowest excited triplet energy level of the exciplex is greater than 0 eV and not more than 0.2 eV.
A light emitting element characterized by the above. In claims 1 to 20,
The guest material emits light;
A light emitting element characterized by the above. In any one of Claims 1 to 21,
The guest material is
One or more skeletons selected from anthracene, tetracene, chrysene, pyrene, perylene, and acridone;
One or more substituents selected from aromatic amines, alkyl groups, aryl groups,
A light emitting element characterized by the above. In claim 22,
The skeleton is
Bonded to the substituent,
A light emitting element characterized by the above. In claim 23,
The skeleton is
It binds to the two substituents, and the substituents have the same structure;
A light emitting element characterized by the above. A light emitting device according to any one of claims 1 to 24;
With color filters, seals, or transistors,
A display device. A display device according to claim 25;
A housing or touch sensor;
Electronic equipment having A light emitting device according to any one of claims 1 to 24;
A housing or touch sensor;
A lighting device.